The article presents some sections of the method of calibration of measuring instruments of low absolute pressures (vacuum), used in the research department of state standards in the field of pressure measurement of D. I. Mendeleyev Institute for Metrology (VNIIM), the design and composition of the reference SI used in installations of the 1st and 2nd categories are described, the procedure for determining the basic metrological characteristics and evaluation of calibration results is shown.