Decision rules and guard bands

For an introduction to limits, uncertainty and pass/fail decisions, read Tolerances and decision rules.

A conformity result must explain why a point passed, failed, was indeterminate, or was not evaluated. A controlled decision rule records the exact acceptance logic used alongside the tolerance, measured error, uncertainty, guard band, acceptance interval, outcome, and rationale.

Metra distinguishes the tolerance interval from the acceptance interval. A guard band can make the acceptance interval narrower than the tolerance interval.

For example, an error of +0.430 °C lies inside a tolerance of -0.500 °C to +0.500 °C. With a 0.100 °C guard band, the acceptance interval is -0.400 °C to +0.400 °C, so the point fails.

The controlled types are simple acceptance, a fixed absolute guard band, and a multiplier of selected uncertainty. Each revision also declares one tolerance-shape policy and whether uncertainty is unused, combined standard, or expanded. Metra does not provide a vague formula called only “ILAC G8”; an organisation may cite ILAC G8 as guidance while defining its exact controlled method.

Metra calculates outcomes on the server. Never infer a conformity result by comparing displayed rounded values.

Controlled revisions can be edited while draft. A later revision is created as a new draft and approved independently, preserving every historical assignment and result.

Next: Author and approve a decision rule, then assign the approved revision.