A comparison measurement among two different gas flow meters calibration systems with different traceability is presented. The measurements were conducted in the Zagreb gasworks laboratory on The basic testing system, Bell prover and System for calibration great flows. System for calibration great flows has traceability to National institute for metrology of Netherlands – VSL, and Bell prover to The basic testing system of Zagreb gasworks. The basic testing system has traceability through the physical value of mass according to the National institute for metrology of Slovenia – MIRS. Results of each systems are processed with a rules for interlaboratory comparisons and the Guidelines for the measurement uncertainty. For the comparison of calibration results was used normalised factor EN. The stated measurements are conducted with the aim of checking the ability of the IRMS G16 gas meter to transfer the physical values flow and volume to the gas flow meters calibration systems. Until now, the transfer of physical values flow and volume in Zagreb gasworks was conducted with the gas meter wit the fluid NB2, which could not be used for technical reasons at that time. The performances and characteristics of the gas as an energy source are described, the types of gas flow meters are explained and described, as a principles of the rotary displacement gas meters, which are used in this thesis. The principles of the gas flow test systems, which are calibrated by gas meters are presented. The procedures and calibration instructions for these systems are explained and procedures for calculating standard deviations and measurement uncertainty, as well as the basic characteristics of these systems. Additional calibrations with the rotary displacement gas meter IRMA G16 checked the matching of the gas flow meters calibration systems in Zagreb gasworks with National institute for metrology of Netherlands – VSL.