Sum all the resulting digits (including the ones that were not doubled).
# The check digit is calculated by , where s is the sum from step 4. This is the smallest number (possibly zero) that must be added to to make a multiple of 10.
# Other valid formulas giving the same value are , , and . Note that the formula will not work in all environments due to differences in how negative numbers are handled by the modulo operation.

Example for computing check digit

Assume an example of

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