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.
Left side (odd parity) codes
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
0
1
2
3
4
0001101
0011001
0010011
0111101
0100011
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
5
6
7
8
9
0110001
0101111
0111011
0110111
0001011
Right side (even parity)
codes
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
0
1
2
3
4
1110011
1100110
1101100
1000010
1011100
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
1
2
3
4
5
6
7
5
6
7
8
9
1001110
1010000
1000100
1001000
1110100
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:
In other words, suppose you want to find
the check digit of UPC barcode number 7-26412-17542. Step 1: From the right to the left,
start with odd position, assign the odd/even
position to each digit: 7-26412-17542 (odd
positions are in red). Step 2: Sum all digits in odd position
and multiply the result by 3. (7+6+1+1+5+2)
x 3=66 Step 3: Sum all digits in even position.
(2+4+2+7+4)=19 Step 4: Sum the results of step
three and four: 66+19=85 Step 5: Divide the result of step
four by 10. The check digit is the number
which adds the remainder to 10. In our
case, divide 85 by 10 we get the remainder
5. The check digit then is the result of 10-5=5.
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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