Whenever any single-bit error occurs in a transmission block of data, such two-dimensional parity checking, or "two-coordinate parity checking", enables the receiver to use the TRC to detect which byte the error occurred in, and the LRC to detect exactly which track the error occurred in, to discover exactly which bit is in error, and then correct that bit by flipping it.
Set LRC = 0 For each byte b in the buffer do Set LRC = (LRC + b) AND 0xFF end do Set LRC = (((LRC XOR 0xFF) + 1) AND 0xFF)
which can be expressed as "the 8-bit two's-complement value of the sum of all bytes modulo 28" (
x AND 0xFF is equivalent to
x MOD 28).
An 8-bit LRC such as this is equivalent to a cyclic redundancy check using the polynomial x8 + 1, but the independence of the bit streams is less clear when looked at in that way.