API MPMS Chapter 12, Part 2 is a multi-part publication that consolidates and standardizes calculations pertaining to metering petroleum liquids using turbine or displacement meters and clarifies terms and expressions by eliminating local variations of such terms. The purpose of standardizing calculations is to produce the same unbiased answer from the given data. For different operators to obtain identical results from the same data, the rules for sequence, rounding and discrimination of figures (or decimal places) must be defined.

This part provides standardized calculation methods for the quantification of liquids and the determination of base prover volumes under defined conditions, regardless of the point of origin or destination or units of measure required by governmental customs or statute. The criteria contained in this document allow different entities using various computer languages on different computer hardware (or manual calculations) to arrive at identical results using the same standardized input data.

This document also specifies the equations for computing correction factors, rules for rounding, including the calculation sequence, and discrimination levels to be employed in the calculations. No deviations from these specified equations are permitted, since the intent of this document is to establish a rigorous standard.