The United States Pharmacopeia (USP) is the single reference work for the quality control of drugs in the United States. It is therefore also binding for pharmaceutical companies in other regions of the world who export into the US market.

• USP Chapter 41 "Balances” is mandatory and states the requirements for balances used for materials that must be accurately weighed. It does not cover balances used for manufacturing.
• USP General Chapter 1251 "Weighing on an Analytical Balance" is informational, detailing the state-of-the-art for analytical balance weighing. It supplements Chapter 41 but also applies to balances used in analytical procedures beyond Chapter 41's scope

USP General Chapter 41 explicitly states that the measurement uncertainty must be reported in a calibration certificate. It emphasizes that all measurement devices, including balances, have inherent measurement uncertainty. Calibration is essential to quantify the accuracy of weighing results by determining this uncertainty. The measurement uncertainty provides a plus/minus range around each weighing result. Our Accuracy Calibration Certificate (ACC) fulfils this mandatory requirement. 

For the first time in a Pharmacopoeia, in the USP Chapter 1251, the concept of a safety factor is explicitly introduced for balances and also quantified:

• 2 for stable laboratory conditions and trained operators
• 1.5 for automated weighing procedures (e.g., gravimetric dosing)

A safety factor helps ensure that the required accuracy of a balance is not compromised over time. It accounts for any changes in the performance of a balance due to wear and tear, changing external influences such as drafts, vibrations, or temperature fluctuations, and operator variability. In other words, it is a margin added to the minimum weight.

USP 41 does not provide specific guidance on the exact frequency of performing performance checks. But it states that the frequency of both calibrations and performance checks should be determined based on a risk-based approach. This means that companies must assess the risks associated with their weighing applications and set appropriate intervals accordingly. The emphasis is on tailoring the frequency to the quality and risk requirements rather than following fixed intervals.