Calibration Interval and Mandatory Periodic Recalibration / Mandatory Periodic Verification
ILAC-G24:2007 / OIML D 10:2007 (E)
"An important aspect for maintaining the capability of a laboratory to produce traceable and reliable measurement results is a determination of the maximum period that should be permitted between successive calibrations (recalibrations) of the reference or working standards and measuring instruments used."
National Research Council, "Discussion on calibration intervals"
Period of time or amount of use between calibrations
To ensure equipment remains reliable
National Research Council, "Recommended practices for calibration laboratories"
Intervals of calibration
Test equipment and measurement standards should be calibrated at periodic intervals established and maintained to assure acceptable measurement uncertainty and reliability. Intervals should be shortened or may be lengthened when the results of previous calibrations indicate such action is necessary or sufficient to maintain acceptable reliability. ISO 10012-1 Annex A and NCSLI RP-1 Establishment and Adjustment of Calibration Intervals contain guidelines for the determination of calibration intervals for measuring equipment.
Reliability means the probability of equipment remaining in tolerance during the calibration interval, and for standards, the probability of the assigned value of the standard not changing by more than the list of uncertainties. In the client's laboratory, the list of uncertainties should include any uncertainty associated with drift rate.
R. v. Jackson, 2015 ONCA 832 (CanLII)
 ... A new instrument, not due for its first annual inspection. ...
R. v Vallentgoed and Gubbins, 2016 ABCA 358 (CanLII)
Facts in Vallentgoed
detained May 11, 2013
Certificate of Annual Maintenance, January 22, 2013 ... that it is “in proper working order and continues to meet the manufacturer’s specifications”.
Repair record for January 30, 2013: The problem was diagnosed as a damaged breath tube connector, which was repaired. The instrument then required recalibration.
Facts in Gubbins in AB PC 2014 ABPC 195 (CanLII)
alleged offence March 10, 2014
the Intox EC/IR II, the type of instrument employed in testing the accused
all service, maintenance and modifications for the Intox EC/IR II are contracted to a third party (Davtech). The breath testing instrument is sent to the service provider when it is due for annual maintenance or when the instrument is indicating an error message.
NASA Measurement Quality Assurance Handbook - Annex 3
Measurement Uncertainty Analysis Principles and Methods, p. 122
"An error or bias in an MPTE [measuring testing equipment] attribute or parameter may increase or remain constant or decrease. The uncertainty in this error, however, always increase with time since measurement or calibration. This is the fundamental postulate of uncertainty growth.”
“Uncertainty growth over time corresponds to an increase in out of tolerance probability over time or equivalently to a decrease in intolerance probability or measurement reliability over time.”
"measurement reliability can be modeled by a time-varying function. Once this function is determined, then MTE parameter bias uncertainty can be computed as a function of time."
Blog articles respecting Calibration Interval