In this experiment X-ray diffraction was used to measure the diffraction spaces of some crystal units, namely MgO, LiF and NaF. Monochromatics X-rays with 0.154 nm wavelength scattered by those crystals according the Bragg's law. Using tel -X-Ometer (Tel 580) it was found that the diffraction space of MgO is 0.456 nm, LiF is 0.415 nm and of NaF is o.458 nm. These results differ from the numbers reported in the Handbook lattice spacing about 8,3 % fo MgO; 2,98% for LiF; and 0,87% for NaF