calculating check digit. formula issue

[harker(Legacy Member)]

Hi

I am obviously not understading the check digit caclulastion for a UPC-13 barcode. or is that EAN-13. Anyway a 13 digit barcode.

I have written something that just makes sure the barcode entered is valid, by chec k the digits against the check digit.

This works with all the barcodes except this one book I have.

the barcode is 9780450022852

now from my understanding if I add the odd digits i get

9+8+4+0+2+8=31

times by 3

31*3 = 93

add the even digits

93+7+0+5+0+2+5=112

the next higher multiple of 10 is 120

120 - 112 = 8

but the barcode check digit is 2

this is for a book as you can see from the 978

This is actually printed on the book and, what's worse, the check digit calculator on this site calcualtes 2 as the check digit, not 8.

Is it actually the nearest multiple rather than the next higher multiple??

please tell my I'm an idiot and have forgotten missed something.

regards

Steve

Edited by harker on June 17 2006 at 2:36am

[glitch (legacy member)]

The check digit is the number whihc adds the remainder to 10. So you need a further step: 10-8=2

See explanation here:

http://www.morovia.com/education/utility/upc-ean.asp