This chapter specifies the characteristics of stationary (fixed) or portable tank provers that are in general use and the procedures for their calibration. Guidelines are provided for the design, manufacture, calibration and use of new and/or replacement tank provers, and are not intended to make any existing tank provers obsolete. More specific design criteria are available in NIST 1 Handbook 105-3, Specifications and Tolerances for Graduated Neck-Type Volumetric Field Standards (includes Provers, per Section 1.1 of NIST 105-3). Consideration must also be given to the requirements of any weights and measures authority that may be involved. 1 National Institute of Standards and Technology, Gaithersburg, Maryland 20899.