19 May
2006
19 May
'06
1:12 a.m.
* mcintosh@servidor.unam.mx <mcintosh@servidor.unam.mx> [May 19. 2006 08:37]:
Quoting "Schroeppel, Richard" <rschroe@sandia.gov>:
Also c. 1965, I was coding some business program for an IBM customer, and was given a check-digit algorithm that alternately added and subtracted digits. Perhaps we took the result mod 10 to get the check; I can't recall.
Isn't this plain old ISBN? The signs alternate to get a modulo 11 sum which is immune to digit switching, a common transcription error, whereas taking a sum modulo 9 is not.
- hvm
wikipedia is often useful with these practical bits: http://en.wikipedia.org/wiki/ISBN