A method of studying the progressive crystal lattice changes occurring in a series of alloys or mixed crystals is described. This method compares the Bragg angles of x‐ray reflection from a standard crystal with those of the crystal being studied. The important features of the method are simplicity and high accuracy (0.002 percent), which is attained without the use of an accurately calibrated angle scale. The theory of the method is discussed and two examples of experimental data which have been obtained are given.