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Hello I need to check that the NHS numbers in my database are valid. I''m storing them as ten-digit strings: the first nine are the identifier and the tenth is a check digit. There are four steps to calculating the check digit (from http://www.connectingforhealth.nhs.uk/systemsandservices/nsts/docs/tech_nn_check_digit.pdf): 1. multiply each of the first nine digits by a weighting factor (10 for the first digit, 9 for the second... 2 for the ninth) 2. sum the results of these multiplications 3. divide the total by 11 and establish the remainder 4. subtract the remainder from 11 t...