is the premier technical standard used to quantify this accuracy. The ASME PTC 19.1 PDF provides comprehensive procedures for evaluating uncertainty in test measurements and propagating them into final results.

What (e.g., temperature, pressure, flow) are you measuring?

The standard provides rigorous equations to combine these into and then Expanded Uncertainty (usually at 95% confidence).

Understanding ASME PTC 19.1: The Standard for Test Uncertainty