What is the 11th Number?
If the code is only meant to be known by certain people (e.g. members of a fan club), rather than worked out, the 11th digit could be a 'check digit'. A check digit is used to authenticate a code and is worked out by performing a calculation on the code itself. The two most common check digit algorithms are the Modulo 10 algorithm and the Modulo 11 algorithm. For details on how to work out a check digit click here.
