Andrew Welch wrote:
> to give you the check-digit?  If so it makes the outermost "mod 10" of
> $calc redundant?  (if it is then step #4 on the wikipedia article isnt
> needed)

It is needed for calculating the check digit, in the special case that
the steps 1..3 produce 10 (which is, if the $totalsums mod 10 equal 0).
10 is not allowed as digit. Doing modulo 10, will give 0.