Pass/Fail Criteria

Pass/fail criteria establish the boundaries for declaring whether an instrument conforms to its specifications. These criteria typically consist of the tolerance limits for each measurement parameter and the decision rule that defines how measurement uncertainty is considered in the determination. The criteria must be clearly defined in the calibration procedure before calibration begins.

The simplest approach uses the manufacturer's specified tolerance as the pass/fail boundary, without accounting for measurement uncertainty (simple acceptance). More rigorous approaches incorporate decision rules that consider measurement uncertainty, such as guard-banding (narrowing acceptance limits to control false accept risk) or the approach specified in ANSI/NCSL Z540.3 (limiting the probability of false accept to 2% per tolerance limit).

For calibration management, pass/fail criteria must be documented, traceable to requirements, and consistently applied. The criteria may come from multiple sources: manufacturer specifications, industry standards, customer requirements, or engineering specifications. When multiple sources exist, the most stringent criteria typically apply. Calibration software should enforce the correct criteria for each instrument type and automatically flag results that fall outside the acceptance limits. Clear documentation of pass/fail criteria on calibration certificates provides transparency to the customer and supports audit compliance.