A method of measuring differences in lattice spacing with an accuracy of 1 part in 108in a period as short as two minutes is described. The method uses one source of copper radiation and a triple‐axis arrangement. Two of these axes are double‐leaf silicon springs in monolithic crystal assemblies which achieve the high stability required by such measurements. Samples are easily changed and sequences of measurements are performed entirely under computer control. The method is demonstrated by a comparison of the lattice spacings of four samples which reveals differences of up to 60 parts in 108between silicon crystals of different orig