|
|
|
|
|
|
|
|
|
 |
 |
 |
|
|||||
 |
 |
|
||||||
 |
|
 |
|
How They Work
Barcodes were originally invented to help supermarkets speed up their check out process, but it was such a good system that it soon spread to all other products too.
Barcodes are made up of a series of black and white stripes and some numbers. The stripes actually say the same thing as the numbers, but in a way that is easier for computers to read. Each number from 0 to 9 is made up of black and white stripes of different thicknesses, arranged in different orders.
Most barcodes are made up of 12 numbers. The first number identifies what type of product it is – here it is 1. The next six numbers are the manufacturer number – they identify the company that made the product. In the barcode above, the manufacturers number is 34567. Any product made by this company will start with this number.
The next five numbers make up the product number. This number identifies the particular product, and will be different for every product made by a company. In the above barcode, the product number is 89012.
The last number is called the check number – here it is 2. You’ll have seen the people who work in shops ‘scan’ barcodes with a device that shines out a red light onto the barcode. These ‘scanner’ machines read the barcode, and the check number allows them to work out if the number has been scanned correctly or not. The way that they check them is quite complicated, but is also very clever. Here’s how the check number is calculated for the barcode above:
1. Add together all of the numbers in odd positions (the 1st, 3rd, 5th, 7th, 9th and 11th numbers). So 1+4+6+8+0+2=21
2. Multiply that number by 3. 3x21=63
3. Add together all of the numbers in even positions, except for the check number (the 2nd, 4th, 6th, 8th and 10th numbers). 3+5+7+9+1=25
4. Add the total from step 2 to the total from step 3. 63+25=88
5. 5. Take this number, and work out which number needs to be added to it to make a number divisible by 10. So here, 2 needs to be added to 88 to make 90 (90 divided by 10 = 9). The number you add will be the same as the check number if the barcode has been scanned correctly.
Try this with the barcodes of things you buy to see if it works.