A method of determining an offset, modulo n, of at least one point with respect to a sequence 50 of at least n symbols, the sequence consisting of a repeating codeword of a cyclic position code, the cyclic position code having length n and minimum distance d.sub.min, the method including: obtaining, from the sequence 50 and at a position corresponding to the at least one point, a subsequence 52 of length w symbols, where w.gtoreq.n-d.sub.min+1; mapping the subsequence 52 to a codeword 58 of the cyclic position code most likely to match the subsequence in the presence of symbol errors 60, 62 in the subsequence; and determining an offset 54, in the sequence 50, of the codeword 58 thus obtained, and thereby determining the offset of the at least one point.