How to read a scope of accreditation
A scope lists, per quantity, the range, the calibration and measurement capability (CMC) and the method. Reading it tells you whether the laboratory can certify what you need — and at what uncertainty.
Accreditation bodies publish each laboratory's scope as a table. For temperature, a typical row reads: 'Platinum resistance thermometers, by comparison in stirred liquid baths, −80 °C to 250 °C, CMC 0.01 °C to 0.02 °C.' Each element constrains what the laboratory may claim.
Reading each column
- Measured quantity / instrument type: what can be calibrated (thermometers, loggers, chambers, indicators).
- Range: the temperatures covered; look for gaps between ranges.
- CMC: the expanded uncertainty (k = 2) the laboratory can achieve for a near-ideal device. ILAC-P14 forbids reporting less than it.
- Method or remarks: comparison, fixed point, simulation; bath or block; immersion conditions.
- Location: permanent laboratory or site; the site CMC is usually larger.
If your logger has 0.1 °C resolution, a laboratory with 0.005 °C CMC gives you no better certificate than one with 0.02 °C — resolution dominates either way.
Frequently asked questions
- What does 'electrical simulation' in a scope mean?
- Calibration of an indicator by injecting a known resistance or voltage instead of a temperature — it calibrates the electronics, not the sensor.
References
- [1]ILAC-P14: ILAC Policy for Measurement Uncertainty in Calibration
- [2]ISO/IEC 17025:2017 — General requirements for the competence of testing and calibration laboratories
General technical guidance written against the cited sources. It is not regulatory or legal advice and does not replace the applicable standard, guideline or a qualified reviewer's judgement.
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What is CMC in calibration?
Calibration and Measurement Capability is a laboratory's best-case uncertainty, not the accuracy of your instrument.
How to choose a calibration laboratory
Check the accreditation scope for the exact quantity, range and uncertainty you need; then evaluate turnaround, certificate quality and how they handle out-of-tolerance findings.