Electron diffraction patterns can be automatically indexed by comparing two nearest diffraction spots with two calculated reciprocal vectors r1* and r2*2, r1*×r2*= Au. However, non-primitive solutions corresponding to non-primitive reciprocal plane cells, sometimes result. For simple Bravais lattices, obviously A=1 is the criterion of primitive solutions. For primitive solutions in centred Bravais lattices, it has been shown that A has also specified values for various combinations of u, v, w indices.