Chapter 5: The Start and Stop Asterisk (*) |
In Brief: The asterisk (*) is the single most recognizable feature of a Code 39 barcode. It is the only character that is both required and forbidden in the data payload. Every valid Code 39 symbol begins with an asterisk and ends with an asterisk. These asterisks are not part of the encoded information; they simply tell the scanner where the barcode starts and stops. This chapter explores why this design choice was made, how the asterisk works at the pattern level, and how this simple framing mechanism has shaped the use of Code 39 across dozens of real-world industries. We will look at practical examples from manufacturing, logistics, healthcare, government, retail, automotive, aerospace, energy, education, and many other fields. Along the way, we will connect the technical properties of Code 39 -- its self-checking nature, its variable length, its narrow-to-wide ratio, its lack of a mandatory checksum, and its bi-directional readability -- to the specific needs of each application. By the end, you will see that the humble asterisk is not a decorative flourish but a foundational element that makes Code 39 robust, simple, and extraordinarily versatile. |
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5.1 The Asterisk as a Framing Marker |
To understand the start/stop asterisk, we must first appreciate a basic problem in barcode scanning: the scanner does not know where the barcode begins or ends when it looks at a label. The laser or camera sees a long string of bars and spaces. Without a marker, the scanner might start reading in the middle, miss the first few characters, or interpret background noise as part of the data. The start and stop characters solve this by providing a unique, unambiguous pattern that cannot appear anywhere else in the symbol. |
In Code 39, the asterisk is encoded as a specific sequence of five bars and four spaces, with exactly three wide elements and six narrow elements. This pattern is chosen so that it is not confused with any of the 43 data characters (digits 0-9, uppercase A-Z, and seven special symbols). The scanner locks onto this pattern, reads outward from it, and knows that the data lies between the two asterisks. Once it hits the second asterisk, it stops decoding. |
Crucially, the asterisk is excluded from the data character set. You cannot encode an asterisk as actual information in a Code 39 barcode. This is a hard rule. If your inventory system has an item named 'Product *123', you must either omit the asterisk or use a different barcode symbology. This restriction is not a bug; it is a deliberate safety measure. Because the asterisk is reserved for framing, the scanner never has to guess whether a given asterisk pattern is data or a boundary. This eliminates a whole class of decoding errors. |
The asterisk also enables bi-directional reading. Since the same pattern appears at both ends, a scanner can read the barcode from left to right or right to left. The decoded string will be reversed internally, but the scanner software flips it back because it recognizes that the asterisks are the endpoints. This is a huge advantage in high-speed conveyor belts or handheld scanning where the operator might not present the label in a perfect orientation. |
Another subtle benefit is that the asterisk provides a known reference for the narrow-to-wide ratio. Code 39 uses two widths of bars and spaces: narrow and wide. The wide elements are typically 2 to 3 times the width of the narrow ones. The asterisk pattern contains both wide and narrow elements in a fixed arrangement. When the scanner reads the start asterisk, it measures the relative widths and calibrates itself for the rest of the symbol. This makes Code 39 tolerant of print quality variations, different printer resolutions, and uneven surfaces. |
Now, let us explore how these technical properties -- anchored by the asterisk -- translate into practical advantages across a broad spectrum of industries. |
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5.2 Manufacturing and Assembly Lines |
Manufacturing is the birthplace of Code 39, and the asterisk plays a central role in keeping production lines moving. In automotive plants, for example, engine blocks, transmissions, and chassis components are tracked through dozens of machining stations. Each part carries a metal or polyester label with a Code 39 barcode. The start and stop asterisks ensure that even if the label is smudged with oil, partially covered by a clamp, or read at a skewed angle, the scanner can still find the framing markers and extract the part number. |
Consider a real scenario: a cylinder head casting moves along a conveyor. At each station, a laser scanner reads the barcode to log the time, station ID, and quality check results. The barcode might be only 12 characters long, encoding a work order and a sequence number. The asterisks at both ends mean that the scanner does not need to know the length in advance. It simply looks for the first asterisk, reads until it finds the second asterisk, and reports the data in between. This variable-length capability is critical because different parts have different numbering schemes -- some have 8 characters, some have 15, and some have alphanumeric prefixes. |
In heavy machinery manufacturing, components are often large and stored outdoors. Labels may fade under sunlight or get covered in dust. The asterisk's robust pattern, with its three wide elements, remains detectable even when the contrast is poor. Workers use handheld scanners with red lasers, and the scanners are programmed to emit a beep only after they have successfully found both start and stop asterisks. This audible feedback confirms that the entire barcode was captured, not just a fragment. |
Another manufacturing use case is work-in-progress tracking. A fabricated metal bracket might travel through welding, painting, and inspection. Each operator scans the barcode to pull up digital work instructions. Because the asterisk is never part of the data, there is zero risk of a scanning error where a data character is mistaken for a delimiter. This might seem trivial, but in high-volume production, even a 0.1% error rate can cause hundreds of misrouted parts per day. The asterisk eliminates that specific failure mode. |
The self-checking property of Code 39 also comes into play here. Each character in Code 39 has its own parity -- exactly two wide bars and one wide space, or vice versa, depending on the character. The scanner can verify each character as it decodes. If one character fails the parity check, the scanner knows immediately and can trigger a re-read. The asterisk itself follows the same parity rule, so if the start marker is corrupted, the scanner will not attempt to decode the rest. This prevents partial reads that could lead to incorrect inventory updates. |
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5.3 Logistics and Warehouse Distribution |
In the logistics industry, Code 39 barcodes are ubiquitous on shipping labels, pallet tags, and shelf labels. The start/stop asterisk is especially valuable here because packages move at high speed through sortation systems. Tunnel scanners, which are arrays of lasers arranged around a conveyor, read barcodes from any angle. The asterisk's bi-directional property means that a package can be placed on the belt facing forward or backward -- the scanners will still decode the barcode correctly. |
A major parcel carrier processes millions of packages per night. Each package has a Code 39 label that encodes a tracking number, usually 10 to 20 alphanumeric characters. The label also includes a human-readable interpretation below the barcode. The asterisk is printed as a visible star character at both ends, so warehouse staff can visually confirm the start and end of the barcode. This visual cue is surprisingly helpful for manual sorting when scanners are temporarily unavailable. |
In distribution centers, workers use wearable ring scanners or Bluetooth-enabled handhelds to pick items from shelves. The picking list shows a barcode for each storage bin. When the worker scans the bin, the system confirms they are at the correct location. The asterisk ensures that the scanner does not accidentally read a partial barcode from an adjacent label. Because the scanner waits for the start asterisk, it ignores random bars and spaces that might appear from damaged labels or reflective surfaces. |
Cross-docking operations also benefit from the asterisk's calibration function. In cross-docking, incoming trucks are unloaded and outgoing trucks are loaded within hours. Labels are often printed on demand using thermal printers. Print quality can vary due to ribbon wear, print head dust, or poor media. The asterisk provides a consistent reference for the narrow-to-wide ratio. If the printer produces wider-than-normal bars, the scanner adjusts its thresholds based on the start asterisk and applies the same scaling to the entire barcode. This adaptive decoding reduces re-scans and keeps the dock flowing. |
Another logistics application is yard management. Trailers and containers are tagged with Code 39 labels that identify the asset. These labels are exposed to rain, mud, and freezing temperatures. The asterisk pattern is relatively simple and resistant to distortion. Even if a space is partially filled with dirt, the scanner can still recognize the wide/narrow sequence. This ruggedness is a direct result of the design choice to use only two widths, which was itself enabled by the framing asterisk that anchors the decoding algorithm. |
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5.4 Healthcare and Medical Device Tracking |
Hospitals and clinics rely on Code 39 for patient identification, specimen labeling, and medical device inventory. The start/stop asterisk is critical in this environment because patient safety depends on absolute accuracy. A misread barcode could lead to the wrong medication, the wrong blood transfusion, or the wrong surgical implant. |
In many hospitals, patient wristbands carry a Code 39 barcode that encodes the patient's medical record number. The asterisk at both ends makes the barcode easy to scan even when the wristband is wrinkled or the patient is moving. Nurses scan the wristband before administering any drug, and the system checks the medication against the patient's electronic health record. The self-checking nature of Code 39, combined with the unambiguous framing, gives nurses confidence that the scanner has read the entire barcode. |
Specimen collection is another area where the asterisk shines. Blood tubes, urine cups, and biopsy containers are labeled with Code 39 barcodes that link the sample to the patient. These labels are small, often only 2 inches wide. The variable length of Code 39 allows the lab to use short codes (e.g., 8 characters) for routine tests and longer codes (e.g., 20 characters) for research samples, all without changing the symbology. The asterisk does not take up much space, so even on a tiny tube, the barcode remains readable. |
Medical device manufacturers use Code 39 to track surgical instruments, implants, and diagnostic equipment. Each device is etched or laser-marked with a barcode that includes a catalog number and serial number. Laser marking on metal surfaces produces low-contrast marks, but the asterisk's robust pattern is still decodable. Sterilization processes, such as autoclaving and ethylene oxide treatment, do not degrade the barcode significantly because the marking is permanent. The start and stop asterisks survive repeated cleaning cycles without fading. |
Pharmacy automation systems also use Code 39 for unit-dose packaging. Each pill blister or vial has a barcode that encodes the National Drug Code. The asterisk helps the scanner differentiate between the barcode and other printing on the package, such as lot numbers and expiration dates in human-readable text. This is particularly important when packages are cluttered with warnings and logos. The scanner simply looks for the unique asterisk pattern and ignores everything else. |
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5.5 Government and Military Applications |
Government agencies and military organizations adopted Code 39 early because of its simplicity, reliability, and open standard. The Department of Defense in the United States used Code 39 for many years under the LOGMARS (Logistics Applications of Automated Marking and Reading Symbols) program. The start/stop asterisk was a key factor in this adoption because military supply chains operate in harsh environments -- desert heat, arctic cold, jungle humidity, and battlefield dust. |
In military logistics, every piece of equipment from a rifle to a radar system is barcoded with a unique identifier. The asterisk allows the barcode to be read from any direction, which is essential when soldiers are wearing gloves and cannot rotate a label. The bi-directional feature also means that a handheld scanner can be aimed casually; the software will automatically orient the data. |
Government property management uses Code 39 for asset tags on computers, furniture, vehicles, and office equipment. These tags are often placed on curved surfaces or corners. The asterisk's pattern tolerates slight curvature because the wide-to-narrow ratio is determined locally at the start of the symbol. Even if the barcode is wrapped around a pipe, the start asterisk calibrates the scanner for that specific angle and distance. |
Voting systems in some jurisdictions have used Code 39 on ballot envelopes and poll worker badges. The asterisk prevents accidental reading of stray marks or pre-printed text. Election officials appreciate the simplicity of Code 39 because it does not require expensive proprietary scanners; any standard laser scanner works. The asterisk also makes it easy to visually verify that a label is complete -- you can see the stars at both ends with your naked eye. |
Law enforcement agencies use Code 39 on evidence bags, firearm tracking, and prisoner identification. The start/stop characters ensure that evidence logs are not corrupted by partial scans. In forensic labs, barcodes are scanned repeatedly as samples move through DNA analysis, toxicology screening, and fingerprint matching. The asterisk's reliability reduces chain-of-custody errors, which are critical in court proceedings. |
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5.6 Retail and Point-of-Sale |
While Code 39 is not the primary symbology for supermarket checkout (UPC-A holds that role), it is widely used in retail for shelf labels, price tags, and store loyalty cards. The start/stop asterisk is beneficial here because retail environments are filled with reflective surfaces, competing graphics, and variable lighting. |
Many department stores use Code 39 for in-store inventory management. When new stock arrives, each item receives a price tag with a Code 39 barcode that encodes the stock-keeping unit (SKU) and sometimes a color/size code. The asterisk ensures that the scanner reads the entire SKU, not just a fragment. This is especially important for items with long SKUs that include alphabetic characters (e.g., 'SHIRT-BLUE-L') because Code 39 natively supports uppercase letters without special encoding. |
Loyalty cards often use Code 39 to encode a customer ID. The barcode is printed on the back of the card, and the asterisk appears at both ends. When a customer presents the card at checkout, the cashier scans it, and the system applies discounts or accumulates points. The variable length allows different retailers to use different ID lengths -- some use 10 digits, some use 16 alphanumeric characters. The asterisk makes the barcode self-framing, so the same scanner can read all variations without reconfiguration. |
Price verification is another retail application. Store associates carry handheld scanners to check shelf prices against the central database. The shelf labels have Code 39 barcodes that encode the item number. The asterisk allows the associate to scan quickly without carefully aligning the scanner. They can swipe the scanner across the label at an angle, and the start asterisk will still be detected first. This speeds up price checks during busy hours. |
In warehouse clubs and bulk retail, pallets are labeled with Code 39 barcodes that contain case quantities and lot numbers. The asterisk pattern is large enough to be read from a distance of several feet using long-range scanners. The self-checking feature ensures that the scanner does not misinterpret a damaged space as a wide element, which could change the entire data string. This reduces the need for manual entry of lot numbers, saving time and reducing human error. |
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5.7 Automotive Industry |
Beyond manufacturing, the automotive industry uses Code 39 in dealerships, service centers, and parts warehouses. The start/stop asterisk is crucial for tracking vehicle identification numbers (VINs), which are 17-character alphanumeric codes. Since Code 39 can handle uppercase letters and digits, it is a natural fit for VINs. |
At a car dealership, every new vehicle has a barcode label on the windshield or door jamb. When the vehicle is sold, the salesperson scans the barcode to register the sale, transfer warranty information, and schedule the first service. The asterisk ensures that the entire VIN is captured, even if the label is partially obscured by a sunshade or a dealer sticker. The scanner reads from the first asterisk to the second asterisk, so it does not accidentally include extra text printed near the label. |
Service departments use Code 39 on repair orders and parts tags. When a mechanic replaces a part, they scan the barcode on the old part and the new part to update the vehicle history. The asterisk allows the barcode to be printed on small adhesive labels that fit on tiny components like sensors and fuses. The variable length is helpful because part numbers range from 6 to 18 characters, and Code 39 accommodates all of them without padding. |
Parts warehouses for automotive aftermarket distribution rely heavily on Code 39. Shelves are lined with bins, each displaying a barcode that encodes the bin location. Pickers scan the bin barcode and then scan the part barcode to confirm a match. The asterisk prevents cross-scanning between adjacent bins because the scanner only starts decoding when it sees the start asterisk. If the laser sweeps across two labels, it will typically miss the start asterisk of the second label and produce no read, prompting the picker to try again -- rather than picking the wrong part. |
In vehicle registration and title transfer, some state DMVs use Code 39 on temporary tags and inspection stickers. The asterisk's visual star symbol helps clerks manually key in the number if the barcode is unreadable due to wear. This fallback is important because DMV clerks are not always trained on barcode technology, but they can easily identify the asterisk as the delimiter. |
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5.8 Aerospace and Defense |
The aerospace industry demands extreme traceability for every component that goes into an aircraft. From rivets to avionics, each part must be tracked through manufacturing, maintenance, and overhaul. Code 39 is widely used for this purpose, and the start/stop asterisk is a key enabler. |
Aircraft maintenance, repair, and overhaul (MRO) facilities use Code 39 to track parts during engine teardown and reassembly. Each fan blade, turbine disc, and fastener has a barcode that encodes a unique serial number and revision level. The asterisk ensures that the scanner reads the entire code, even when the part is oily or covered in carbon deposits. The bi-directional reading capability is useful because mechanics often scan parts in tight spaces where they cannot flip the label around. |
The Federal Aviation Administration (FAA) has specific advisory circulars that recommend barcode standards for aircraft parts. Code 39 is often specified because of its maturity and reliability. The asterisk's self-clocking nature means that the scanner does not rely on a separate clock signal; it extracts timing from the bar and space widths starting from the first asterisk. This is important in aerospace because laser marking on titanium or aluminum creates low-modulation marks that can fool more complex symbologies. |
Defense contractors use Code 39 for munitions tracking, radar systems, and communication equipment. The start/stop characters provide a clear delimiter that is resistant to electronic interference. In military depots, scanners are often ruggedized and operate in dusty, windy conditions. The asterisk pattern is simple enough that even with a partially dirty scanner window, the framing markers are detectable. |
Another aerospace application is baggage tracking at airports. While IATA (International Air Transport Association) has moved toward two-dimensional barcodes for boarding passes, many airlines still use Code 39 on baggage tags for internal routing. The asterisk allows the baggage handling system to read tags that are crumpled, twisted, or folded. The scanners on the conveyor belts are tuned to detect the start asterisk first, then decode the 10-character baggage number, and then look for the stop asterisk. If the stop asterisk is missing due to damage, the scanner will not output a partial number, preventing misrouted luggage. |
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5.9 Energy and Utilities |
The energy sector -- oil and gas, electricity, water, and renewable energy -- relies on Code 39 for asset management and safety compliance. The start/stop asterisk is particularly valuable in outdoor environments where labels are exposed to extreme weather, chemicals, and UV radiation. |
In oil refineries, pipes, valves, and pumps are labeled with Code 39 barcodes that encode equipment numbers and inspection dates. The asterisk allows the barcode to be read with a long-range scanner from a safe distance, avoiding hazardous areas. The bi-directional feature means that a technician can scan the label from either side of a pipe, which is convenient when access is restricted. |
Electrical utilities use Code 39 on utility poles, transformers, and substation equipment. Field crews scan these barcodes with rugged handheld computers to record maintenance activities. The asterisk ensures that the scan is complete, even if the label is partially covered by vines or snow. The self-checking parity prevents the scanner from misreading a character due to a dirty space, which could otherwise lead to working on the wrong piece of equipment. |
Water treatment plants use Code 39 for pump stations, chemical tanks, and flow meters. The labels are often printed on vinyl or polyester with permanent adhesives. The asterisk pattern is large enough to be read from arm's length, reducing the need for ladders or scaffolding. Variable length is useful because different assets have different naming conventions -- some use a 5-character code, others use a 12-character alphanumeric string. |
Renewable energy installations, such as wind farms and solar arrays, also employ Code 39. Each wind turbine has a barcode that encodes the turbine serial number and GPS coordinates. The asterisk makes the barcode readable even when the label is mounted on a curved nacelle. Solar panel strings are labeled with barcodes that link to performance monitoring systems. The start and stop asterisks ensure that data from each string is accurately associated with the correct inverter. |
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5.10 Education and Library Systems |
Libraries were among the early adopters of Code 39 for book tracking. The start/stop asterisk is a familiar sight on library book spines. Each book has a barcode that encodes a unique accession number. The asterisk allows the librarian to scan books quickly during checkout and check-in. |
In school and university libraries, self-checkout kiosks use Code 39 barcodes. Students place their student ID and books on the scanner pad. The system reads the asterisk-framed barcodes and updates the circulation database. The bi-directional feature is helpful because books can be placed on the pad in any orientation. The asterisk also prevents the scanner from reading the ISBN or other printed numbers nearby, as those are not framed by asterisks. |
Educational institutions use Code 39 for equipment tracking as well. Laptops, projectors, microscopes, and sports equipment are labeled with barcodes. The asterisk ensures that when a teacher checks out a laptop, the correct asset is recorded. Variable length allows the school to use short codes for common items and longer codes for specialized lab equipment. |
Exam answer sheets sometimes use Code 39 to identify the student. The barcode is printed on the sheet, and the asterisk helps the scanning machine locate the barcode amidst printed instructions and grid lines. This is particularly important in high-stakes testing, where a misread could invalidate a student's score. The self-checking property adds an extra layer of verification. |
Public libraries that share inter-library loan systems use Code 39 on transit labels. The asterisk is recognized by multiple vendors' scanners, making Code 39 a lingua franca for library automation. Even though libraries are gradually moving to Code 128 or Data Matrix for space efficiency, Code 39 remains widespread because of its simplicity and the trust that librarians place in the asterisk. |
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5.11 Transportation and Tolling |
Transportation systems, including toll roads, bridges, and public transit, use Code 39 for vehicle identification and fare collection. The start/stop asterisk is essential for high-speed vehicle tracking where the scan time is measured in milliseconds. |
Electronic toll collection systems often use windshield-mounted transponders, but many also have Code 39 barcodes as a backup. When a vehicle passes through a toll lane, a camera reads the barcode sticker on the windshield. The asterisk allows the system to quickly locate the barcode in the camera image, even with reflections from the sun or headlights. The bi-directional feature ensures that the vehicle can be read whether it enters the lane from the left or right. |
Public transit buses and trains have Code 39 labels on the exterior for fleet management. Maintenance crews scan these labels during routine inspections. The asterisk helps the scanner work in rainy or snowy conditions, where water droplets on the label can distort the bars. The self-checking mechanism rejects any character that does not conform to the parity rule, so a partially occluded label produces a no-read rather than a wrong read. |
Parking garages use Code 39 on parking tickets and monthly passes. The ticket has a barcode that encodes the entry time and a unique token. When the driver exits, the gate scanner reads the barcode. The asterisk ensures that the entire token is captured, even if the ticket is crumpled. This reduces the number of tickets that are rejected, improving customer satisfaction. |
Shipping ports and rail terminals use Code 39 on shipping containers and railcars. The asterisk allows the barcode to be read from a distance of up to 15 feet using fixed-mounted scanners. The variable length is important because container numbers have different formats depending on the shipping line. The start and stop asterisks also help the system distinguish between the container barcode and other markings on the container, such as weight limits and hazard labels. |
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5.12 Food and Beverage Industry |
The food and beverage industry uses Code 39 for traceability, inventory rotation, and quality control. The start/stop asterisk is valuable in cold storage and wet processing environments. |
In food processing plants, raw materials such as flour, sugar, and oil arrive in bulk containers with Code 39 labels. The asterisk allows the scanner to read the label even if it is frosty or covered in condensation. The bi-directional feature means that a forklift driver can scan the label from either side of a pallet without turning around. |
Batch tracking is a legal requirement in many food sectors. Each batch of finished product gets a Code 39 barcode that encodes the production date, line number, and batch code. The asterisk ensures that the scanner reads the full batch code, which is critical for recalls. If a contaminant is found, the manufacturer can trace every unit back to the exact production hour. The self-checking property reduces the chance of a corrupted batch code leading to an incomplete recall. |
Beverage distributors use Code 39 on kegs, cases, and pallets. The asterisk helps the scanner cope with wet, slippery labels that might be smeared by spilled drinks. The narrow-to-wide ratio calibration from the start asterisk adapts to labels that have stretched slightly on curved keg surfaces. This adaptability is a direct benefit of the asterisk's role as a calibration anchor. |
Restaurant supply chains use Code 39 for inventory management of perishable goods. Each item in a walk-in cooler has a barcode that encodes the item number and expiration date. The asterisk makes the barcode scannable even when the label is crumpled or partially torn. Staff can quickly scan items during stocktaking, and the system highlights expired products. The variable length allows different suppliers to use their own coding schemes without coordination. |
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5.13 Pharmaceutical and Laboratory Research |
Pharmaceutical companies and research laboratories rely heavily on Code 39 for sample tracking, compound management, and regulatory compliance. The start/stop asterisk is a cornerstone of their barcode strategy because accuracy is paramount. |
In drug discovery, millions of chemical compounds are stored in microtiter plates. Each plate has a Code 39 barcode that encodes a plate ID and well format. The asterisk ensures that automated plate handlers can read the barcode reliably, even when plates are stacked or moving rapidly. The bi-directional property allows the reader to work in both directions, which is useful in robotic systems that shuttle plates back and forth. |
Clinical trial supplies are labeled with Code 39 to maintain blinding and randomization. Each kit has a unique code that is linked to the patient and the treatment arm. The asterisk prevents the scanner from reading a partial code, which could break the blind. The self-checking mechanism adds an extra verification step before the system dispenses the medication. |
Laboratory information management systems (LIMS) use Code 39 on sample tubes, slides, and petri dishes. The asterisk allows the barcode to be scanned through the plastic rack or even through a thin layer of ice. The start and stop characters are printed slightly larger than the data characters in some implementations, making them easier to locate manually. This is a design choice that leverages the asterisk's dual role as a machine-readable marker and a human visual cue. |
Regulatory bodies like the FDA and EMA require robust traceability for drug products. Code 39's asterisk provides a simple, standardized framing that is accepted across multiple countries and languages. Because the data is alphanumeric, it can accommodate national drug codes, lot numbers, and expiration dates in a single symbol. The asterisk ensures that the scanner does not confuse the barcode with other printed information, such as corporate logos or pictograms. |
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5.14 Electronics and Semiconductor Manufacturing |
Electronics manufacturing uses Code 39 on printed circuit boards (PCBs), components, and finished goods. The start/stop asterisk is essential because PCBs are often small and densely populated, leaving limited space for barcodes. |
PCB manufacturers laser-etch Code 39 barcodes directly onto the board surface. The asterisk pattern is designed to be readable even with low-contrast laser marks on copper or solder mask. The self-checking property allows the scanner to verify each character, which is important because a single misread could cause the board to be populated with the wrong components. The asterisk's framing ensures that the scanner does not accidentally read the board's edge markings or test points. |
Component trays and reels use Code 39 labels that encode part numbers and quantity. The asterisk allows the scanner to read the label even when the reel is spinning at high speed during automated assembly. The bi-directional feature means that the scanner can read the label whether the reel is oriented left-to-right or right-to-left, which simplifies loading. |
Semiconductor test houses use Code 39 on wafer cassettes and probe cards. The asterisk helps the scanner read through the transparent plastic cassettes, which can cause reflections. The narrow-to-wide calibration from the start asterisk compensates for any distortion caused by the plastic. This enables fully automated testing without human intervention. |
Consumer electronics manufacturers use Code 39 on final assembly labels for serial numbers. The asterisk allows the barcode to be read at the final packing station, where workers scan the barcode to generate shipping labels. The variable length accommodates serial numbers that may have letters and digits, such as 'SN-A1234-5678'. The asterisk provides a clear visual boundary, so workers can easily see where the barcode begins and ends. |
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5.15 Security and Access Control |
Security systems use Code 39 on employee badges, visitor passes, and asset tags. The start/stop asterisk is valuable because badges are often read in busy environments with multiple scanners and interference. |
Employee ID badges often have a Code 39 barcode on the back. When an employee enters a secure area, they swipe the badge through a slot reader or present it to a proximity reader. The asterisk ensures that the reader captures the entire employee ID, which typically includes a department code and a sequential number. The self-checking feature prevents a dirty badge from being misread, which could allow unauthorized access or deny entry to an authorized person. |
Visitor management systems print temporary badges with Code 39 barcodes that encode the visitor's name, host, and expiration time. The asterisk allows the receptionist to scan the badge quickly during check-in and check-out. The bi-directional property means the badge can be scanned from either side, which is convenient when the visitor is wearing the badge on a lanyard. |
Asset tracking for high-value items like laptops, projectors, and art works uses Code 39. The asterisk makes the barcode scannable even if the label is partially hidden under a security cable or protective case. Security guards perform random audits by scanning assets and comparing them to a database. The start and stop asterisks reduce false reads, so the audit is accurate and efficient. |
Some correctional facilities use Code 39 on inmate wristbands and cell doors. The asterisk ensures that the scanner reads the entire inmate number, which is critical for headcounts and medication distribution. The ruggedness of Code 39 means the barcode survives rough handling and frequent cleaning. |
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5.16 Telecommunications and Data Centers |
Telecom companies and data centers use Code 39 for server rack identification, cable labeling, and equipment inventory. The start/stop asterisk is helpful in crowded racks where labels are packed closely together. |
Each server in a data center has a Code 39 barcode on the front bezel. The asterisk allows remote hands technicians to scan the barcode using a handheld scanner or a mobile phone camera. The variable length is useful because server serial numbers can be 7 to 15 characters long, and they often include letters. The self-checking property ensures that the technician does not misread a zero as an 'O' or a one as an 'I', which are common errors in manual entry. |
Cable labeling is a notorious challenge in data centers. Fiber optic and copper cables have small wrap-around labels with Code 39 barcodes. The asterisk pattern is printed large enough to be visible, even on narrow labels. The bi-directional feature allows the scanner to read the label regardless of which way the cable is facing. This speeds up troubleshooting and moves, adds, and changes (MAC) operations. |
Telecom central offices use Code 39 on distribution frames, power panels, and transmission equipment. The asterisk enables the barcode to be read from a distance using a telescoping scanner, which is safer than climbing ladders. The narrow-to-wide calibration adapts to labels that have been stretched or shrunk due to temperature variations in the equipment room. |
Inventory audits in data centers rely on Code 39 to reconcile physical assets with asset management systems. The asterisk provides a reliable framing marker, so the audit team can scan hundreds of racks without frequent no-reads. This efficiency translates to lower labor costs and higher uptime. |
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5.17 Agriculture and Forestry |
Agriculture and forestry use Code 39 for tracking livestock, crops, equipment, and timber. The start/stop asterisk is valuable in outdoor environments with mud, dust, and vegetation. |
Cattle ranchers use Code 39 ear tags on livestock. Each tag encodes a unique animal ID. The asterisk allows the farmer to scan the tag from a distance using a long-range reader, reducing stress on the animal. The bi-directional property is useful because the animal may turn its head, changing the tag's orientation. The self-checking feature prevents misreads that could mix up pedigree records. |
Crop management systems use Code 39 on irrigation valves, sprayer tanks, and harvesting bins. The asterisk ensures that the scanner reads the correct bin number when produce is weighed and graded. Variable length accommodates different farm coding systems -- some use simple numbers, others use alphanumeric plot codes. |
Forestry operations use Code 39 on trees that are marked for harvest, as well as on logs and lumber. The asterisk allows the barcode to be printed on weather-resistant labels that are stapled to stumps or painted on logs. The start and stop asterisks help the scanner differentiate the barcode from bark texture and saw marks. Timber inventory is critical for sustainable forestry, and the asterisk contributes to accurate volume calculations. |
Greenhouses and nurseries use Code 39 on plant tags. Each tag encodes the cultivar, batch number, and planting date. The asterisk allows the scanner to read the tag even when it is wet from watering. The narrow-to-wide calibration compensates for labels that have curled or wrinkled in humid conditions. |
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5.18 Construction and Building Materials |
The construction industry uses Code 39 for tracking materials, tools, and safety inspections. The start/stop asterisk is essential on job sites where labels are exposed to concrete dust, paint, and weather. |
Structural steel beams and precast concrete panels are labeled with Code 39 barcodes. The asterisk allows the scanner to read the label from a distance using a laser rangefinder scanner. The bi-directional feature is useful because beams are often rotated during lifting. The self-checking property ensures that the scanner does not misread a character due to dust or weld spatter. |
Tool tracking on construction sites uses Code 39 on drills, saws, and generators. The asterisk ensures that the tool is correctly checked out and returned. Variable length allows the tool ID to include a category code and a serial number. The rugged labels survive drops and chemical exposure. |
Safety inspection tags on scaffolding, cranes, and hoists use Code 39. The asterisk helps the inspector scan the tag quickly and record the inspection date. The start and stop asterisks provide a visual reminder that the tag is a valid barcode, not just a random sticker. |
Building material suppliers use Code 39 on pallets of bricks, tiles, and lumber. The asterisk enables the forklift driver to scan the pallet label without getting off the vehicle. The narrow-to-wide calibration adapts to labels that have been crushed or folded during transport. |
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5.19 Postal and Courier Services |
Postal services and courier companies use Code 39 on mail pieces, parcels, and sortation bins. The start/stop asterisk is a key enabler of high-speed automated sorting. |
In postal processing plants, letters and flats are sprayed with Code 39 barcodes that encode the delivery address. The asterisk allows the sorting machine to read the barcode at speeds of over 10 feet per second. The bi-directional property means the machine can read the barcode regardless of the envelope's orientation in the feeder. The self-checking feature rejects any character that is misread due to ink splatter or paper dust. |
Courier companies use Code 39 on waybills and shipping labels. The asterisk ensures that the tracking number is fully captured when the package is scanned at each checkpoint. The variable length is important because tracking numbers vary by service level -- express, ground, and international all have different formats. The start and stop asterisks also help the scanner distinguish the barcode from the address block and promotional text. |
Return labels for e-commerce often use Code 39. The asterisk allows the customer to scan the label at a drop-off location, and the system updates the tracking status. The self-checking property provides confidence that the return is correctly associated with the original order. |
Postal automation also uses Code 39 on tray tags and container labels. These labels encode the destination sort center and the batch number. The asterisk allows the scanner to read the label even if it is partially covered by stretch wrap. This reduces mis-sorts and improves delivery accuracy. |
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5.20 Summary of Technical Properties and Their Industry Impact |
We have journeyed through nearly twenty industries, and a clear pattern emerges: the start/stop asterisk is not a minor detail but a central design feature that makes Code 39 suitable for a stunning variety of applications. Let us now summarize the technical properties we have discussed and explicitly connect each to the real-world benefits observed in the field. |
First, the asterisk provides an unambiguous framing marker. Because the asterisk is excluded from the data set, scanners can reliably locate the beginning and end of the barcode. This eliminates partial reads and cross-talk between adjacent labels. In manufacturing, this means components are not misrouted. In healthcare, it means patients receive the correct treatment. In logistics, it means packages reach the right destination. The practical consequence is a dramatic reduction in data entry errors compared to manual keying or less robust symbologies. |
Second, the asterisk enables bi-directional reading. The same pattern at both ends allows the scanner to decode the barcode from either direction. This is invaluable in conveyor systems, handheld scanning, and robotic automation. In postal sorting, it allows high-speed processing without reorienting items. In retail, it speeds up checkout. In aerospace maintenance, it allows mechanics to work in cramped spaces. The asterisk thus directly contributes to operational efficiency and user convenience. |
Third, the asterisk serves as a calibration reference for the narrow-to-wide ratio. By measuring the widths of the elements in the start asterisk, the scanner adjusts its internal thresholds to compensate for print quality variations, label stretching, and viewing angle. This makes Code 39 remarkably tolerant of less-than-perfect printing and harsh environments. In oil refineries, it works despite chemical exposure. In food processing, it works despite condensation. In agriculture, it works despite mud. This robustness reduces scanner no-reads, which translates to fewer manual interventions and lower labor costs. |
Fourth, the asterisk is part of Code 39's self-checking architecture. Each character, including the asterisk, contains a fixed number of wide and narrow elements. The scanner verifies each character on the fly. If a character fails the parity check, the scanner can immediately signal an error. This is a first-line defense against corrupted data. In pharmaceutical labs, it prevents misidentified samples. In military logistics, it maintains the integrity of supply chains. In tolling systems, it ensures vehicles are billed correctly. The asterisk itself is verified first, so the scanner never wastes time on a symbol that does not even have valid framing. |
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Fifth, the asterisk's visual presence is a human-friendly feature. The star symbol is easily recognizable, even to untrained eyes. Warehouse workers, librarians, nurses, and clerks can quickly tell where the barcode starts and ends. This aids in manual backup when scanners fail and provides a simple quality check -- if you do not see two asterisks, the label is likely truncated or damaged. This visual cue is often overlooked in technical discussions, but it is a major reason why Code 39 has remained popular for decades. |
Sixth, the asterisk supports variable length encoding without any preamble or length field. The scanner simply decodes characters between the two asterisks until it reaches the stop marker. This means a single scanner configuration can handle barcodes of any length from 1 to 43 characters (or more with extended Code 39). In practice, this allows organizations to adopt Code 39 for a wide range of identifiers without redesigning their label formats. In data centers, it accommodates different serial number lengths. In libraries, it works for both short accession numbers and long barcode strings with prefixes. |
Seventh, the asterisk makes Code 39 a 'self-clocking' symbology. The timing information is derived from the bar and space widths, starting from the asterisk. There is no separate clock track. This simplifies the scanner hardware and reduces cost. Low-cost laser scanners and even smartphone cameras can decode Code 39 reliably. This affordability has democratized barcode technology, enabling small businesses, schools, and non-profits to adopt automatic identification without large capital investment. In developing countries, Code 39 is often the first barcode symbology introduced because of its low entry barrier. |
Eighth, the asterisk contributes to the overall simplicity of Code 39. With only 43 characters plus the asterisk, the encoding and decoding logic is straightforward. This simplicity means that firmware for scanners is easy to implement, test, and verify. Manufacturers can produce scanners that are highly reliable across many use cases. It also means that software developers can easily generate Code 39 barcodes in any programming environment -- a single lookup table suffices. This simplicity has led to widespread adoption in open-source projects and custom applications. |
Now, let us consolidate all these technical advantages into a final, comprehensive summary that ties together the entire chapter. |
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Final Comprehensive Summary |
The start and stop asterisk (*) is the defining hallmark of the Code 39 barcode. It is not a decorative afterthought; it is a deliberate, engineered feature that solves multiple problems simultaneously. By reserving the asterisk exclusively for framing, the designers of Code 39 created a symbology that is self-framing, bi-directional, self-calibrating, self-checking, human-readable, variable-length, self-clocking, and simple to implement. These properties are not abstract academic curiosities -- they are the very reasons why Code 39 has thrived for over five decades in a dizzying array of industries. |
In manufacturing, the asterisk ensures that engine blocks and circuit boards are never misidentified, even on dirty or curved surfaces. In logistics, it enables high-speed sortation and error-free warehouse picking. In healthcare, it protects patient safety by delivering complete, uncorrupted reads of wristbands and specimen labels. In government and military, it provides reliability under the most extreme conditions. In retail, it speeds up inventory and loyalty transactions. In automotive, it tracks vehicles from assembly to service. In aerospace, it maintains the strict traceability required for airworthiness. In energy, it helps manage assets in hostile environments. In education and libraries, it simplifies the tracking of books and equipment. In transportation, it supports tolling and parking with rapid, accurate reads. In food and beverage, it enables batch traceability and recall readiness. In pharmaceuticals, it underpins clinical trials and regulatory compliance. In electronics, it works on tiny boards with low-contrast marks. In security, it protects access control and asset audits. In telecommunications, it organizes data centers and cable plants. In agriculture, it tracks livestock and crops in the open field. In construction, it withstands dust and heavy handling. In postal and courier services, it powers sorting machines that process millions of items daily. |
Across all these domains, the asterisk performs the same fundamental function: it tells the scanner where the barcode begins and ends. But the secondary effects of that function -- calibration, reversal tolerance, parity checking, visual verification, length flexibility, and cost efficiency -- are what make Code 39 so adaptable. No other symbology offers such a perfect balance of simplicity and robustness in a single framing character. |
The asterisk also serves as a pedagogical tool. For anyone learning about barcodes, the asterisk is the first thing they see and the first concept they understand. It demystifies the technology: a barcode is just a sequence of characters between two stars. This intuitive grasp lowers the learning curve for operators, technicians, and managers alike. It is no accident that Code 39 is often the first symbology taught in barcode training courses. |
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Looking to the future, Code 39 will likely continue to be used alongside newer symbologies like Code 128 and Data Matrix. Those symbologies offer higher density, error correction, and Unicode support. However, they are more complex and require more sophisticated decoding algorithms. Code 39's asterisk-based framing remains a gold standard for applications where simplicity, readability, and cost are paramount. In many niches, especially in developing economies and legacy systems, Code 39 is not going away anytime soon. |
Moreover, the asterisk has cultural resonance. In common typography, the asterisk is a star, a symbol of attention and reference. In barcodes, it has become a symbol of reliability and universality. When you see a Code 39 barcode, the two asterisks at the ends are like friendly bookends, assuring you that the information inside is complete and ready to be read. That assurance is the foundation of trust in automatic identification systems. |
In conclusion, the start and stop asterisk is much more than a delimiter. It is the architectural pillar upon which Code 39's success is built. It enables a symbology that is forgiving of print imperfections, tolerant of reading angles, resistant to partial reads, and affordable for all. The asterisk has been scanned billions of times in factories, hospitals, warehouses, and stores around the world. Each scan begins with a star and ends with a star, a silent ritual that powers global commerce and safety. Understanding the asterisk is understanding the soul of Code 39. And as we have seen through dozens of practical examples, that soul is woven into the fabric of modern industry, from the deepest mines to the highest skies, from the smallest pill bottle to the largest cargo ship. The humble asterisk, in its quiet way, has earned its place in the pantheon of great engineering solutions. |
cs@easiersoft.com