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A bar code secret

To get a really accurate measurement of the bar width of your bar codes, you should verify them using an approved bar code verifier which will give you the full analysis of bar width, contrast, potential light margin errors and the rest of the measurements which gives you your CEN/ANSI/ISO grade. However, there is a little trick that ‘not a lot of people know’ which involves only visual inspection, which can be a handy tool……


The guard bars in a EAN 8, EAN 13, UPC A & UPC E code (these are the ones, 3 pairs, which are a little longer than the other bars in your code) are comprised of three elements – bar, space, bar – these three elements should be the same width.


Just RightJustRightToo FatTooFatToo Thin

Why is bar width important..?

Bar codes are made up of bars and spaces and the width of those elements is critical for the formation of each digit within your 8 or 13 digit code. The contrast difference between bars and spaces is also what a machine depends upon to decode the bar code number – this may seem blindingly obvious and it’s only when you study a reflectance profile ( a graph which denotes in essence, how a scanner ‘sees’ a code) that with some codes, the difference is not sufficient between bars and spaces, to read the number! If you imagine the bars getting wider and wider, squeezing the spaces tighter and tighter, eventually the space becomes too small and the reflectance of that space becomes lower – in other words it appears grey or black. Alternatively, if your bars become too thin, your code becomes difficult to print

What should you do about bar width errors…?

It depends on how your bar codes were generated. In the ‘real world’ bar code examples above, the centre one (‘too fat’) was produced on a thermal printer onto a tag – you may well produce these in your business. Quite often, when bars are too wide, turning down the burn temperature on your print head, will result in a thinning of the bars. If they are too thin, turn up the temperature.


If your codes have been supplied by an artwork house and are outside the specification, you may need to have a word with your printer to make sure that sufficient bar width gain has been accounted for (or loss, with some printing techniques)


As a rule of thumb, it is better to be a little on the thin side than too wide. Also, try to standardise on a minimum of 100% magnification factor for all of your codes – that way, you have a greater tolerance for bar width variance.

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