Back With CRC we have a generator polynomial which will divide into a received value. If we receive a remainder of zero, we can determine there are no errors. We must then calculate the required remainder from a modulo-2 divide and add this to the data, in order that the remainder will be zero when we perform the divide.
To take a simple example, we have 32, and make it divisible by 9, we add a ‘0’ to make ‘320’, and now divide by 9, to give 35 remainder 4. So lets add ‘4’ to make 324. Now when it is received we divide by 9, and if the answer is zero, there are no errors, and we can ignore the last digit.