The Check digit is a validation; ie check, that the vin is correct:
If trying to validate a VIN with a check digit, first either: (a) remove the check digit for the purpose of calculation; or (b) utilize the multiplicative property of zero in the weight to cancel it out. You should later compare the original value of the check digit with the calculated value. If the two values do not match (and there was no error in the calculation), then there is a mistake in the VIN. However, a match does not prove the VIN is correct, because there is still a 1 in 11 chance of any two distinct VINs having a matching check digit.
with that explanation...it's a mathematical equation...
I'll bet that makes it clear as mud...