1. Check that the certificate belongs to the right instrument
Compare the instrument name, make, model and serial number on the document with your instrument. Pay particular attention to the serial number if you have several instruments of the same model. Also check the certificate number, calibration date and issuing organisation.
2. Look at the values used for calibration
Calibration points show the values at which the instrument was checked. For example, a thermometer may have been calibrated at 0 °C, 50 °C and 100 °C. Check whether these points and the stated environmental conditions are adequate for your intended use. Looking only at the instrument’s measuring range is not enough.
3. Understand measurement error with an example
The reference value is the value used for comparison. The instrument indication is the value your instrument displays. For example, if the reference is 100.0 °C and the thermometer displays 100.4 °C, it reads 0.4 °C high at that point. If error is defined as instrument indication minus reference, the error is +0.4 °C and the corresponding correction is −0.4 °C. Check the column headings, sign conventions and units on the certificate. Do not assume that this example correction applies at every temperature.
4. Understand what measurement uncertainty means
Measurement uncertainty expresses how precisely a result can be stated. It is neither the instrument’s error nor the permitted error limit. Read the reported uncertainty value, its unit and any explanation of the coverage factor (k) together. In your own use, the environment, measurement method and operator may also contribute to uncertainty.
5. Assess whether the result meets your needs
An acceptance criterion is a limit defined in advance for your measurement. When comparing results with this limit, also apply the decision rule that specifies how measurement uncertainty is taken into account. If the certificate states conformity, check which limit and rule it uses. Without such a statement, the instrument is not automatically unsuitable; the results need to be assessed for your intended use. Ask the calibration provider or your quality representative about anything unclear.
6. Add your assessment to the instrument record
Keep the certificate with the instrument record. Record who reviewed it, the review date, the decision on use and the next follow-up date. If the results do not meet your defined limits, stop using the instrument and inform the responsible person. Also investigate whether previous measurements made with it may have been affected.
Further reading
For metrology concepts, consult JCGM publications, and for calibration intervals, consult ILAC guidelines . This article provides general information; assessments specific to your equipment and process must consider the applicable requirements.