FIGI — Detail checksum differentiation

Raised by Tom Rutt:

6.1.2 Character 12: the final paragraph states the the algorithm has been adjusted to result in a different checksum value from the "standard" algorithm. Where is this standard algorithm specified? Is it annex C of ISO 6166? If so the differences are not explained in the FIGI spec. The 6166 algorithm doubles the alternating digits starting from the rightmost, this seems to be the same algorithm as used by FIGI.

Detail checksum algorithm

Clarify the origin and differentiation of the checksum algorithm in contrast to other established algorithms. This requires the following changes to section 6.1.2 (at the very end of the section):
1. replace "algorith" with "algorithm" in the first sentence of the last paragraph (typo correction, but in context).
2. add the sentence "A familiar instantiation of this algorithm is specified in ISO 6166 and is used in generating the check digit for ISIN identifiers." as the second sentence of the last paragraph.
3. add " In particular, rather than multiplying the integer value corresponding to every second character starting with the second character in the identifier by two, as is the case with this specification, the ISIN specification begins with the first character. The result is that the check digit is different in over 90% of the logically possible strings ." as a new last sentence of the last paragraph.