A master prover is required in the method to determine a K-factor or meter factor for the master meter. This meter factor and/or Kfactor are used to determine the field prover’s volume. Prover volume determinations using the master meter method are only as accurate as the calibration performed on the master prover. The master prover volume shall be determined per the current API Chapter 4.9 and 12 standards and must be traceable to NIST or appropriate NMI. Errors in the master prover calibration directly transfer to the volume of the field prover.

The master meter chosen for this method must produce good reproducibility and repeatability throughout its operating range. The API standards require run repeatability no higher than 0.02% for five consecutive runs and 0.02% deviation between meter factor averages for the pre and post runs sets at the same flow rate. The performance of the master meter should essentially remain unchanged throughout the meter proving runs. Master meter placement should be close coupled to the field prover to create a single unit with the master prover. It is typically referred to as the master meter prover system. Trimet is supplying different type of Master meter in calibration industry using Emerson Coriolis flow meter , Emerson Turbine flow meter and PD flow meters.