This part of ISO 18213 presents statistical procedures that can be applied to tank calibration and volume measurement data for nuclear materials accountancy tanks. In particular, this part of ISO 18213 presents a) several diagnostic plots that can be used to evaluate and compare tank calibration data; b) a procedure for estimating the uncertainties of tank calibration measurements (i.e., determinations of height and volume); c) a model for estimating either a tank’s calibration equation or its inverse (the measurement equation), together with related uncertainties, from a set of standardized tank calibration data (i.e., from a series of standardized height-volume determinations); d) a method for computing uncertainty estimates for determinations of liquid volume. It is intended that the methods in this part of ISO 18213 be used within the context of the other parts of ISO 18213. Specifically, the methods presented in this part of ISO 18213 are tailored to the general methodology described in ISO 18213-1 and to appropriate related algorithms in ISO 18213-2, ISO 18213-4, ISO 18213-5 or ISO 18213-6. Although the methodology in this part of ISO 18213 is intended for application specifically within the context of the other parts of ISO 18213, the methods are more widely applicable. In particular, the statistical model presented in Clause 6 for estimating the tank's measurement equation from a set of standardized calibration data can be applied, regardless of whether or not these data are acquired in accordance with the methods of ISO 18213. A similar statement holds for (propagation) methods of variance estimation: it is intended that the results in this part of ISO 18213 be applied to the specific models for which they were derived, but the methods themselves are more widely applicable.