a_ud (8/21/2012)

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Thanks Sean. By now I've got a very clear idea of what the (mod 23) code does in SQL (code in VBA still pending).

Basically it takes a number 'ID' like '1234' and calculates the following in each iteration 'i':

i | mod | mod + i*substring(id,i1)
1 | 0 0+1 *1=1
2 | 1 | 1+2*2 = 5
.........
7 | .... | 30

Then 30 mod 23 = 7 --> and 7+1 would be the value used for looking up the corresponding letter, an H ("ABCDEFGHJKLMNPQRSTVWXYZ"). This can be translated into VBA relatively easily, since Substring is equivalent to Excel function Mid.

Hope this helps someone, a.

a_ud (8/21/2012)

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It's quite standard (at least in Europe!), it's basically a check letter that you generate for verifying a sequence of numbers (like the control digit in a check, a barcode, or a letter for an ID card).

Once you've got the final mod and letter (for '1234' was H), you'd add that to the sequence of nos. So the full check-ID number would read: 1234-H.

Some devices like barcode readers might have code checking that the letter matches the nos, that's all...