The specified product limit and the acceptance boundary used by a decision rule need not be identical. If a guard band is used, its purpose and basis should be explicit.
ILAC's 2019 decision-rule guidance discusses guard bands and acceptance limits. ILAC — Decision Rules and Statements of Conformity (2019).
Ask which boundary applies
For a laboratory statement, distinguish the actual requirement from the rule used to evaluate the measured result. Do not silently rewrite the product specification when explaining the decision.
Keep the basis documented
Use the applicable agreed method and competent analysis. No universal guard-band size is proposed here. The relevant question is whether the rule and its risk treatment fit the intended conformity statement and are understandable to the recipient of the report.
Source reviewed 25 October 2026. Interpretation and original diagrams: PLUSHIP / Qunhe. Examples are illustrative.
Related reading
Rounding Should Follow the Applicable Reporting and Decision Basis
A Result Near a Limit Needs a Defined Decision Rule