Every
product has its fingerprint!
"If
it exists, bar code it"
- Unknown author
On
October 20, 1949, N. J. Woodland and B. Silver
filed a patent application titled "Classifying
Apparatus and Method". The inventors described
their invention as relating "to the art
of article classification [...] through the
medium of identifying patterns". The barcode
is born... Barcodes, of course, are those ever-familiar
'bars' and 'numbers' on virtually everything.
Barcodes represent numbers as a series of vertical
lines. Each of the lines is either black or
white, and the sequence of lines forms a pattern
which is recognized as a particular digit when
scanned by a computer. A single barcode digit
represents actually 7 units or bits. For instance,
the digit '1' is composed of the seven units,
'0011001' or "space-space-bar-bar-space-space-bar".
Every product is assigned a unique 12 or 13-digit
number.
On a UPC barcode the same digits on the left-hand
side (Manufacturer Code) is coded differently
than the digits on the right-hand side (Product
Code). The left side digits are actually the
'inverted' or 'complementary' codes of the right
side digits. The right-side codes are called
even parity codes because there is an even number
of 'black bar' units. The left-side is called
odd-parity because there is an odd number of
'black bar' units. Having different coded numbers
for each side allows the barcode to be scanned
in either direction.
The following table features the left and right
side codes matching the corresponding digits,
separated into seven single units or bits.
Anatomy
of a bar code
Guard Bars are located at the beginning, middle
and end of the barcode. The guard bars indicate
the computer-scanner when the manufacturer and
product code begin and end. The 3 guard bars
are also the supposedly "666" (Number
of the Beast!) hidden in the barcode. But is
the number 666 truthfully hidden in the UPC
barcode? Technically, no it isn't. The digit
6 and the three guard bars 'appear' to be identical,
but they are different: the beginning and ending
guard bars are encoded as '101'; and the middle
guard bar, as '01010'. The digit 6 is a 7-unit
code '1010000'. The beginning and ending guard
bars are only three units, and middle guard
bar is only five units. So, from a computer's
perspective the number "666" is NOT
in the UPC barcode!
Check digit: Also called the 'self-check' digit.
The check digit is on the outside right of the
barcode. The check digit is an "old-programmer's
trick" to validate the other digits (manufacturer
and product code) were read correctly.
How the computer calculates the check digit
Below is the mathematical formula to calculate
the check digit:
More
barcodes
There are many different types of barcodes.
Each uses a series of varying width bars and
spaces to encode numbers and/or letters and/or
special characters. Some barcode symbologies
were designed to encode only numbers while others
can encode numbers. letters and even special
computer control characters.
ISBN
International Standard Book Number includes
the price of the book in the bar code. The last
5 digits in this example translate to $44.95
US dollars.
Data Matrix
Two-dimensional bar code which can store 2,000
ASCII characters. It can encode a lot of information,
in a small space, and adjust to be square or
rectangular.
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