Problems in calibrating standard capacity measures for liquids other than water

The periodic verification of measuring systems for legal volumes of liquids is, generally, more complex than the corresponding laboratory calibration because of the necessity to operate directly in field, without disconnecting the meter from the distribution network. For this reason, guaranteeing a lower uncertainty than the tolerance limits prescribed by the various applicable international standards is often difficult. This paper describes the principal methods (gravimetric and volumetric) for the calibration and verification of standard capacity measures used in the legal control of volumetric meters for liquids other than water, widely used for measuring volumes in commercial transactions and in the fiscal checking of oil products. It also describes the hierarchy of standard capacity measures that guarantees traceability to national standards and that transfers the unit of volume measurement to the primary standards owned by the local metrology authority (CCIAA), and to the working standards used in the field by the authority itself or by the laboratories that maintain and service the measuring systems.