USP Chapter 41: “Balances”
This chapter states the requirements for balances used for materials that must be accurately weighed (see General Notices, 8.20). Unless otherwise specified, when substances must be “accurately weighed”, the weighing shall be performed using a balance that is calibrated over the operating range and meets the requirements defined for repeatability and accuracy. For balances used for other applications, the balance repeatability and accuracy should be commensurate with the requirements for its use. For discussion of the theoretical basis of these requirements, see general information chapter Weighing on an Analytical Balance 1251, which may be a helpful – but not mandatory – resource.