>Does anyone have a routine for calculating mod-7 check digits for barcoding?
>
>Thanks
>
>
>Colin Northway

If it's a EAN-8 or EAN-13 barcode, it's actually a mod-10 check digit, based on a weighted sum of the preceding 7/12 digits - try this page for a description, about 1/2 way down:

http://plus.maths.org/issue12/features/codes/index-gifd.html