Find an item with a 13-digit bar code on it…Eg : 5016442001876

Make a note of the first 12 digits – The 13^th digit is the check digit and this is how to make a bar code calculator to check it.

Put the first 12 digits into the first column of a spreadsheet starting from cell B3 as shown. Draw headings and boxes.

The calculations in column C are…
(Make sure you enter a formula in each cell from C3 to C14).

The digits in cells B4, B6, B8 …(every other digit) are multiplied by 3.

The other digits in cells B3, B5, B7 …remain as they are.

The results are added up in cell C15.

The final calculation in cell C16:

The check digit is the number that needs to be added to the total in cell C15 to make the result an exact multiple of 10.

The formula in cell C16 is this:   =10 – MOD(C15,10)

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