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Re: [Fwd: CAS Numbers]

A question was asked regarding the check digit in
CAS Registry Numbers.  List members may find the
following explanation from CAS Client Services
to be of interest.

Check digits are used by CAS to help ensure the accuracy of CAS
Registry Numbers.  The check digits may be recalculated and
verified any time there is a manual transcription of data, which
creates the possiblity of human error.

The digits preceding the last digit of a CAS Registry Number form a
machine-generated, unique number assigned to a substance at the time of
registration.  The last digit (furthest right) is a check digit computed
algorithmically from the preceding digits.

The check digit is derived as demonstrated below with the CAS Registry Number
for 1-Propanol.

Sequentially assigned registration number = 7123

                      7    1   2   3
Position Multiplier   4    3   2   1
                      28 + 3 + 4 + 3  = 38

The units digit of the resulting number is the check digit.  In this case it
is 8.  Thus the complete CAS Registry Number is 71-23-8.

The hyphens in the CAS Registry Number allow it to be instantly recognized.
Just as the format (XXX) XXX-XXXX is recognized as a U.S. telephone number
and XXX-XX-XXXX is recognized as a social security number.

Eric Shively
CAS Marketing Communications