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CMM Results Near a Drawing Limit: Agree the Decision Rule First
When an order does not state how to handle a reported interval near a drawing limit, acceptance may remain unresolved. This guide helps define the decision rule, report details and escalation path before inspection.
By Geetai Precision
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Why a borderline result needs an agreed rule
An inspection report can show a value and a drawing limit without resolving every acceptance question. If the value lies close to that limit, the buyer and supplier need to know which decision rule governs and what interval information accompanies the report. Set this in the purchase or quality agreement before a disputed part is waiting for disposition.
NIST’s conformity-assessment discussion explains that an acceptance decision rule relates the acceptable-result zone to the zone in which a product characteristic conforms. [1]
NIST describes decision-rule selection as an economic choice that balances the risks of accepting a nonconforming item and rejecting a conforming one. [1]
NIST TN 1297 reporting guidance calls for expanded uncertainty together with its coverage factor, or combined standard uncertainty, and supporting information or a current referenced method. [2]
Put the decision items in the order
Use a short decision sheet with the customer quality or design owner, inspection provider and buyer. The goal is to resolve the reporting and escalation path before the first close-to-limit measurement appears.
| Agreement item | Define in the order | Question to close |
|---|---|---|
| Applicable specification | Drawing revision, characteristic and limits | Which released requirement governs the decision? |
| Decision rule | Named procedure or agreed rule and its scope | How is the reported interval handled? |
| Interval statement | Reported quantity, coverage basis and reference | What supporting method or record accompanies it? |
| Borderline disposition | Review owner, timing and allowed next steps | Who can approve remeasurement, concession or rejection? |
| Record control | Part or lot identity, setup and report revision | Can the decision be traced to the same inspected configuration? |
Do not rely on an informal phrase such as “use the tighter limit” unless the contract defines exactly what that means. If the parties choose a guard band or another boundary, document who selected it and how readings in the outer zone are handled. The commercial allocation should be explicit.
Ask the report to identify the characteristic, drawing reference and value’s relation to the agreed decision procedure. If an interval is stated, explain its meaning and identify a current supporting method. NIST TN 1297 provides reporting guidance; the project must still decide its own acceptance rule.
When a value is close to a limit, pause automatic disposition and follow the agreed escalation route. Review whether the characteristic, datum setup and part configuration match the order. A repeat inspection or alternate method should be authorized and documented; it should not be used selectively to replace an unfavorable result without an agreed basis.
Keep the reported interval distinct from the drawing limit and instrument specifications. Each describes a different part of the decision. An inspection report does not change the drawing, and a calibration record alone does not decide whether the workpiece conforms.
For a drawing review, provide the controlled revision, identify critical characteristics, state who owns acceptance and request a sample report format. Resolve the rule with the responsible quality or engineering authority before production inspection is due.
Inspection scope and documentation are defined during quotation according to drawing requirements and application needs.
References were accessed October 3, 2026. This worksheet is editorial procurement guidance; it does not document results for a specific supplied part.
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References
- Assessment of Conformity, Decision Rules and Risk Analysis — National Institute of Standards and Technology. Accessed 2026-10-02T17:27:51.378Z.
- NIST TN 1297: 7. Reporting Uncertainty — National Institute of Standards and Technology. Accessed 2026-10-02T17:27:51.378Z.