Standard bar code used to identify grocery and other retail merchandise. In the UPC system, the five digits on the left are assigned to a particular manufacturer or maker and the five digits on the right are used by that manufacturer to identify a specific type or make of product.
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The UPC encodes 12 decimal digits as SLLLLLLMRRRRRRE, where S (start) and E (end) are the bit pattern 101, M (middle) is the bit pattern 01010 (called guard bars), and each L (left) and R (right) are digits, each one represented by a seven-bit code. This is a total of 95 bits. The bit pattern for each numeral is designed to be as little like the others as possible, and to have no more than four 1s or 0s in order. Both are for reliability in scanning.
Since S, M, and E all include two bars, and each of the 12 digits of the UPC-A barcode consists of two bars and two spaces, all UPC-A barcodes consist of exactly (3*2)+(12*2)=30 bars.
The UPC has only numerals, with no letters or other characters. The first digit L is the prefix. The last digit R is an error correcting check digit, allowing some errors in scanning or manual entry to be detected. UPC data structures are a component of GTINs (Global Trade Item Numbers). All of these data structures follow the global GS1 standards.
The bar-and-space patterns for each digit 0–9 are as follows:
Before the Middle guard bars, a binary 1 is indicated by a bar, while a 0 is indicated a space. After the Middle guard bars, however, the patterns are optically inverted. In other words, a 1 is now indicated by a space, and a 0 is now indicated by a bar. In the illustration above, the "4" digit (shown in detail), falls after the Middle guard bars, causing the pattern of bars and spaces to be inverted.
In the UPC-A system, the check digit is calculated as follows:
For example, a UPC-A barcode (in this case, a UPC for a box of tissues) "03600029145X" where X is the check digit, X can be calculated by adding the odd-numbered digits (0+6+0+2+1+5 = 14), multiplying by three (14 × 3 = 42), adding the even-numbered digits (42+3+0+0+9+4 = 58), calculating modulo 10 (58 mod 10 = 8), subtracting from ten (10 - 8 = 2). The check digit is thus 2.
|Last digit||UPC-E equivalent is||UPC-A equivalent is|
|0||XXNNN0||0XX000-00NNN + check|
|1||XXNNN1||0XX100-00NNN + check|
|2||XXNNN2||0XX200-00NNN + check|
|3||XXXNN3||0XXX00-000NN + check|
|4||XXXXN4||0XXXX0-0000N + check|
|5||XXXXX5||0XXXXX-00005 + check|
|6||XXXXX6||0XXXXX-00006 + check|
|7||XXXXX7||0XXXXX-00007 + check|
|8||XXXXX8||0XXXXX-00008 + check|
|9||XXXXX9||0XXXXX-00009 + check|
For example a UPC-E barcode with the number 654321 would expand to the UPC-A 065100004327.
UPC-E check digits are calculated using this expanded string in the same way as used by UPC-A. The resulting check digit is not added to the barcode, however, but is encoded by manipulating the parity of the six digits which are present in the UPC-E - as shown in the following tables:
|Check digit||Parity pattern|
|Digit to be encoded||Odd parity pattern||Even parity pattern|
Our example code 654321, therefore, would become 1-1-1 4-1-1-1 1-2-3-1 2-3-1-1 1-4-1-1 2-2-1-2 2-2-2-1 1-1-1-1-1-1. The resulting barcode would look roughly like this:
As the UPC has become technologically obsolete, it is expected that UPC-B and UPC-C will disappear from common use by the 2010s. The UPC-D standard may be modified into EAR 2.0 or be phased out entirely.
UPC-A Bar code symbols can be printed at various densities to accommodate variety of printing and scanning processes. The significant dimensional parameter is called X-dimension, the ideal width of single module element. The X-dimension has to be constant in UPC-A symbol. The width of each bar (dark bar) and space (light bar) is determined by multiplying the X-dimension by the module width of each dark bar or light bar (1,2,3, or 4).
The X-dimension for the UPC-A at the nominal size is 0.33 mm (0.013 in.). UPC-A can be reduced or magnified in the range of 80% to 200%.
Nominal symbol height for UPC-A is 25.9 mm (1.0 in.). In UPC-A the dark bars forming the left, centre, and right Guard Bar Patterns are extended downwards by 5 times X-dimension. This also applies to the bars of the first and the last symbol characters of UPC-A symbol. See illustration.
Quiet Zone (Light Margin)
The minimum Quiet Zone width required by the UPC-A bar code symbol is 9 x X-dimension on both the left and right sides. UPC-E requires 9 X-dimension units on the left side and 7 on the right. (Source; UPC Symbol Specification Manual).
Exactly 12 digits must be printed below the UPC-A barcode.
A group of grocery industry trade associations formed the Uniform Grocery Product Code Council which with consultants Larry Russell and Tom Wilson of McKinsey & Company, defined the numerical format of the Uniform Product Code. Technology firms including Charegon, IBM, Litton-Zellweger, Pitney Bowes-Alpex, Plessey-Anker, RCA, Scanner Inc. and Singer proposed alternative symbol representations to the council. In the end the Symbol Selection Committee chose to slightly modify, changing the font in the human readable area, the IBM proposal designed by George J. Laurer.
Although various companies had UPC Scanning systems in the back of stores, the first UPC marked item ever scanned at a retail checkout (Marsh's supermarket in Troy, Ohio) was at 8:01 a.m. on June 26, 1974, and was a 10-pack of Wrigley's Juicy Fruit chewing gum. The entire shopping cart also had barcoded items in it, but the gum was merely the first one picked up by the cashier. This item is currently on display at the Smithsonian Museum in Washington, D.C.
The UPC Label above shows the general characteristics of Baumeister's proposals. He did not suggest any specific bar code so the image does not attempt to show exact coding of the ten digits required at that time. Also Baumeister's proposal did not include specific guard bars on the sides and center.
A change in management at IBM resulted in Baumiester, Crouse, and Laurer being assigned to different departments. Laurer was give sole responsibility for inventing and creating a viable code and symbol that would satisfy all the requirements. He made several attempts based using the Delta C code invented by Crouse. Finally he devised a new code that also read distances from leading to leading and trailing to trailing edges of bars making it much less sensitive to the printer’s ink spreading degradation. Although this code was based upon the Delta C code, it required far less area. Unfortunately it still did not meet the 1.5 sq. in. requirement. Laurer’s final breakthrough was using the unique characteristics of his new code to invent a way to divide the symbol in halves in such a way that they could be reassembled in the correct order by the scanner. This reduced the necessary area by about 40% to 1.5 by 1.0 inches.
The following table shows the workable labels, available in the early 1970s, with their sizes.
|Check digit||Parity pattern|
|Bulls-eye with Morse Code||Large||Large|
|Bulls-eye with Delta B||12.0" diameter||113.10 sq. in.|
|Bulls-eye with Delta A||9.0" diameter||63.62 sq. in.|
|Baumeister 1st w/ Delta B||6.0" × 5.8"||34.80 sq. in.|
|Baumeister 2 halves w/ Delta B||6.0" × 3.0"||18.00 sq. in.|
|Baumeister 2 halves w/ Delta A||4.5" × 2.3"||10.35 sq. in.|
|Baumeister with Delta C||1.5" × 0.9"||1.35 sq. in.|
This is assuming a Bull’s eye with the same information and reliable readability.
Baumiester and Crouse were no longer involved in the creation of the code and symbol. Crouse was responsible for designing a hand held device to read Laurer’s symbol, Baumiester did theoretical work on scanner designs. D. Savir, a mathematician was given the task of proving the symbol could be printed and would meet the reliability requirements. N. J. Woodland, the inventor of the Bull’s Eye code was responsible for writing the IBM proposal to the selection committee. A group under the direction of Art Hamburgen in Rochester designed and built a prototype scanner incorporating the architecture patented by Laurer. Dr. Sodastrum was the lead engineer on the scanner optics.
December 1, 1972 IBM presented Laurer’s proposal to the Super Market Committee in Rochester Minnesota, the location where IBM would develop the scanner. During the presentation Crouse gave a lab demonstration where he read UPC like labels with a simple hand held wand. In addition to reading regular labels he read the large two page center fold label in the proposal booklet. He then turned to a page showing a photo of labeled items sitting on a table. The labels were small and flawed due to the resolution of the printed photo but the wand read many of them. This demonstration showed the robustness of the code and the proposal was accepted.
Laurer continued his career with the UPC. He became known as the inventor of the UPC; without his persistence there might not have been an IBM proposal. Baumeister and Crouse moved on to other activities, Baumeister prior to the Rochester proposal and Crouse immediately after.
UPC usage notes: