how do UPC bar codes work?

Answer 1

UPC symbol printed on a package has two parts:

The machine-readable bar code
The human-readable 12-digit UPC number
BYG Publishing's manufacturer identification number is the first six digits of the UPC number -- 639382. The next five digits -- 00039 -- are the item number. A person employed by the manufacturer, called the UPC coordinator, is responsible for assigning item numbers to products, making sure the same code is not used on more than one product, retiring codes as products are removed from the product line, etc. In general, every item the manufacturer sells, as well as every size package and every repackaging of the item, needs a different item code. So a 12-ounce can of Coke needs a different item number than a 16-ounce bottle of Coke, as does a 6-pack of 12-ounce cans, a 12-pack, a 24-can case, and so on. It is the job of the UPC coordinator to keep all of these numbers straight!

The last digit of the UPC code is called a check digit. This digit lets the scanner determine if it scanned the number correctly or not. Here is how the check digit is calculated for the other 11 digits, using the code 63938200039 from "The Teenager's Guide to the Real World" example shown above:

Add together the value of all of the digits in odd positions (digits 1, 3, 5, 7, 9 and 11).
6 + 9 + 8 + 0 + 0 + 9 = 32

Multiply that number by 3.
32 * 3 = 96

Add together the value of all of the digits in even positions (digits 2, 4, 6, 8 and 10).
3 + 3 + 2 + 0 + 3 = 11

Add this sum to the value in step 2.
96 + 11 = 107

Take the number in Step 4. To create the check digit, determine the number that, when added to the number in step 4, is a multiple of 10.
107 + 3 = 110
The check digit is therefore 3.

Each time the scanner scans an item, it performs this calculation. If the check digit it calculates is different from the check digit it reads, the scanner knows that something went wrong and the item needs to be rescanned.


As you can see, there is no price information encoded in a bar code. When the scanner at the checkout line scans a product, the cash register sends the UPC number to the store's central POS (point of sale) computer to look up the UPC number. The central computer sends back the actual price of the item at that moment.
This approach allows the store to change the price whenever it wants, for example to reflect sale prices. If the price were encoded in the bar code, prices could never change. On the other hand, not encoding a fixed price gives the store an easy way to rip off customers. When you hear about "scanner fraud" in the news, that is what the newsperson is talking about. It is incredibly easy for a store to mistakenly or purposefully overprice an item.

One thing you will notice if you start looking at UPC codes in detail is that the big manufactures have manufacturer IDs with lots of zeros in them. Here are a few:

Post - 043000
General Mills - 016000
Del Monte - 024000
Quaker Oats - 030000
These short bar codes are called zero-suppressed numbers. There's a set of rules around forming zero-suppressed numbers from full numbers, but the basic idea is to leave out a set of four digits, all zeros. In the case of the Sprite UPC code, the 049 at the beginning is the first three digits of Coke's 049000 manufacturer ID. The 551 is the item number for this bottle of Sprite, shortened from 00551. The zero in the second-to-last digit is the fourth digit from Coke's manufacturer ID. The final digit is the normal check digit. The main reason for having zero-suppressed numbers is to create smaller bar codes for small product packages like 12-ounce cans.

The first digit of the manufacturer's identification number is special. It is called the number system character.

Answer 2

UPC bar codes work very simply. under each bar code is a number, normally its about nine digits. each number is assigned a preset number of bars, whether skinny, fat ones, or a mix. when the laser reader, scans the bar-code it reads the gap or white spaces left by the black bars, which absorb all light. Therefore the laser reads the numbers imprinted on the bottom of the bar code according to the gaps between the lines. a computer system preprograms those numbers with an article (in the store), therefore the store knows which item it just scanned, almost like reading license plates on a vehicle.

Answer 3

How Do Upc Codes Work

Answer 4

How about a simple non wiki copied explanation. Bar codes are a string of binary characters in the form of thick and narrow lines as a laser or ccd scanner passes over this the receptor device (either a simple CCD or other light sensing component and there are a large variation of them) the laser times the light with the light reflection of the surface the amplitude of reflected light as well as this timing tells the software in binary what number is being scanned in which case this is further processed to a simple numeric number usually 9-10 digits in length which is in turn can do 1 of 2 things depending on the size of the merchandiser, in a large company you will have a large network mainframe which the terminal will access for product data and price or for much smaller merchandisers such as small businesses this job is taken over by the terminal which in most cases because of the small inventory requires minimal hard drive space. In either case the delivery process is the same. The fact that this light has to be so carefully times is why checkout laser wands were soon replaced with motorized mirrors as opposed to the cashiers slight of hand.

Answer 5

wish I knew.

Answer 6

It's a little hard to explain without pictures, so check the link below and hopefully that will answer your question. :D

Answer 7

This site has the info you looking for and a video too.
http://electronics.howstuffworks.com/upc.htm