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Check digit [p.k.a. beaten UrQ for sale in Tampa (parts car)]

<<Question, what does the "3" digit after the type 85 mean? Bentley calls it a
check digit. What does that mean?>>

	A digit to verify the authenticity of the serial number.  Not sure how Audi
does theirs, but I am familiar with how it works with UPC symbols.  When UPC
numbers are assigned, the first half is fixed -- the second half you fill in.
Then a check digit is used as the far right-hand number.  When the ten digits
are combined in the prescribed order (odd digits combined in a sequence, even
digits combined in a sequence) they will produce a number.  The check digit is
whatever single digit is needed to cause that value to round up to a product
of 10.  For example, if the number produced is 73, the check digit would be 7.
If the number is 50, the check digit is 0.  Etc., etc.
	(BTW, this is a massive simplification.  The UPC group needs 2-3 pages with
drawings to explain how to do it.....)