1.12: Bravais-Miller indices
The Bravais-Miller indices are used in the case of hexagonal lattices. In that case, one uses four axes, a 1 , a 2 , a 3 , c and four Miller indices, ( hkil ), where h , k , i , l are prime integers inversely proportional to the intercepts OP , OQ , OS , OR of a plane of the family with the four axes. The indices h , k , i are cyclically permutable and related by h + k + i = 0