This part of ISO 8655 specifies a gravimetric reference measurement procedure for the determination of volume of piston-operated volumetric apparatus (POVA). The tests are applicable to complete systems comprising the basic apparatus and all parts selected for use with the apparatus, disposable or reusable, involved in the measurement by delivery (Ex) or contained (In). NOTE General requirements and definitions of terms for piston-operated volumetric apparatus are given in ISO 8655-1. For the metrological requirements, maximum permissible errors, requirements for marking and information to be provided for users for piston-operated volumetric apparatus, see ISO 8655-2 for pipettes, see ISO 8655-3 for burettes, see ISO 8655-4 for dilutors, see ISO 8655-5 for dispensers, and see ISO 8655-9 for manually operated precision laboratory syringes. The photometric reference measurement procedure for the determination of volume of piston operated volumetric apparatus is given in ISO 8655-8. Alternative measurement procedures or the determination of volume are described in ISO 8655-7.