Breaking down the barcode – how do barcodes actually work?

As you can see a single barcode number can actually be broken down into seven separate units – the starting digit or number system character – which tells the scanner where to begin reading the code from, the manufacturer and product code, the check digit, and three guard bars located between these. They let the scanner ‘know’ where the breaks between the codes begin.Keep in mind that the numbers displayed beneath the barcode are not read by the scanner – these are simply for human reference and as a back-up in case the barcode is damaged in some way and the code needs to be entered manually. What the inventory software reads is a binary code related to the width of the black bars and the space in between them. There are 4 different set proportional widths which a barcode can be composed of – a unit which is white displays as space – and registers a 0, a unit which is black registers a 1. This is why barcodes are most commonly black and white as the scanner registers the amount of light which is being reflected by the barcode with a built-in photosensor.

The initial guard bar allows the scanner to calculate the width of one unit, depending on the scale at which the barcode has been printed. The numeral 1 for example is comprised of the code space-space-bar-bar-space-space-bar; or 0011001. The beginning and end guard bars are represented by 101 (bar-space-bar); and the middle guard bar is space-bar-space-bar-space – or 01010.

Additionally, the left and right sides (the manufacturer and product codes) are inverted versions of each other. Basically this means that what was a ‘space’ on one side appears as a ‘bar’ on the other side. Sounds needlessly complicated? Well there’s a nifty trick built in here – this system allows the barcode to be scanned both from right-to-left and left-to-right; which means the code can be scanned in quickly at the till even if the barcode is upside down.

Manufacturer and Product Codes:

The manufacturer code will of course be the same for every barcode assigned to a specific company – the product code will differ for each unique product which they make. In simple terms a company producing a 250ml cooldrink and a 1l version of the same beverage will carry the same manufacturer code but a different product code. If you do the maths the allotted amount of digits means that an individual manufacturer can produce varying barcodes for up to 99 999 unique products!

Check Digit:
The check digit included in a barcode is the final safety test to make sure the barcode has been scanned correctly and is valid. Basically it builds in a mathematical sum which includes all the units of the barcode and comes out at a final answer based on this calculation. The equation is a bit complex but reads as follows – remember not to include the check digit itself!:

a.    Add together all odd digits read
b.    Multiply the final sum of this equation by three
c.    Add all the even digits together
d.    Add together the totals from step b and c
e.    Take this number, and calculate the difference needed to reach the next multiple of ten – this is the check digit. So if your total came to 34, the next multiple of ten would be 40 – making your check digit 6.

The process with an EAN (European Article Number) – which is the 13-digit barcode you may come across in South Africa is slightly different. Starting at the right side of the barcode each digit is assigned with an odd or even position regardless of the number itself. The sum of all the ‘odd’ numbers is then multiplied by three, added to the sum of the ‘even’ numbers and divided by ten. The fraction which is produced – for example 66/10 = 6.6 creates the check digit 4 because 0.4 must be added for there to be no remainder. Makes for a nice party trick if you’re really keen!

Here’s a great video to watch if you want to know more:

In addition to the traditional numerical barcodes you may come across what is called a Code 39 barcode which can also contain alphabetical characters. This system allows for 43 separate characters (Uppercase letters A – Z, numeric digits 0 – 9 and certain punctuation symbols such as $ and %); to be included in the barcode – and rather than the guard bars you find in a UPC or EAN barcode the stops between codes are denoted with an asterisk symbol. Code 128 barcodes even allow for the inclusion of ASCII characters.You may have noticed that no-where in the barcode symbologies we have discussed is the purchase price included in the make-up of the barcode. The cost of a product is designated by the retailer’s database – allowing you to change the price directly with them when need be rather than having to purchase a new barcode each time. For fundamentalist Christians who claim that the ‘New Money System 666’ is discreetly hidden in every barcode; this is where their theory falls flat. However! There has been discussion of personalised barcodes being tattooed onto consumers – allowing their identities to be verified when making a purchase at a retail outlet. This has been claimed to echo the so-called ‘Mark of the Beast’ as mentioned in Revelations in the Bible. Of course, with the exponential increase in consumers purchasing via the internet this system will most likely never come into practice at all. But we’d be interested to hear if our readers would consider getting their own unique identification barcode tattooed? If you’re brave enough to speak up do let us know in the comments!

As always – feel free to get in touch with SA Barcodes about any barcoding questions you may have – we love hearing from you.