This document gives detailed information regarding the evaluation of uncertainty for the gravimetric reference measurement procedure specified in ISO 8655-6[1] and the gravimetric procedure specified in ISO 8655-7:2022[1], Annex A, according to the ISO/IEC Guide 98-3[16]. This document also includes the determination of other uncertainty components related to the liquid delivery process of a piston-operated volumetric apparatus (POVA), e.g. repeatability and handling. Furthermore, it provides examples for the calculation and application of the uncertainty of the mean delivered volume and the uncertainty in use of a single delivered volume.