SC QUALITY GUILDCalibration interval adjustment
SCQUALITYGUILD.COM/TOOLS/CALIBRATION-INTERVAL-ADJUSTMENT.HTML
Use each gauge's as-found calibration history to decide whether to extend, hold or shorten its interval, and see the next due date against a reliability target.
ON THE EXAM · CQI II.F.1, CQT III.C.1, III.C.2 · FREE · NOTHING YOU TYPE LEAVES YOUR BROWSER
Q-BotClick for an explanation of this tool.For educational use. This page is a study aid. The method behind it has far more depth and detail than one page and one tool can cover, and what you see here is not everything the method offers or everything this site offers. For full understanding and application, use the governing standards and texts, and seek further education, training or qualified advice. Results depend on the data you enter, so check them before relying on them.
Why intervals are adjusted
A calibration interval is a bet that the instrument will still be in tolerance when it is next calibrated. Too long, and product is accepted with an instrument that has drifted. Too short, and money is spent calibrating instruments that were fine. ISO 9001:2015 clause 7.1.5.2 requires measuring equipment to be calibrated or verified at specified intervals; it does not set the interval. The evidence for adjusting it is the as-found result: the condition found before any adjustment. The as-left result says nothing about drift.
A common practical method
This tool applies a simple response rule of the kind many labs use: after a set number of consecutive in-tolerance results, extend the interval by a factor; after an out-of-tolerance result, shorten it; otherwise hold. Minimum and maximum limits keep the interval sensible. The number of results and the factors here are example settings, not values from a standard.
Reliability targets and established methods
The reliability target is the share of instruments that should be in tolerance at the end of the interval, set by the lab according to the risk of using an instrument that has drifted. A higher target means shorter intervals. Established methods for setting and adjusting intervals, from reactive rules like the one here to statistical methods that fit a reliability model to the history of a group of similar instruments, are described in NCSL International RP-1, Establishment and Adjustment of Calibration Intervals, and in ILAC-G24 / OIML D 10. Statistical methods need many results; a single gauge with four calibrations gives only a rough indication.
Reading the result
- Extend only on a run of in-tolerance results and an observed in-tolerance rate at or above the target.
- Shorten after an out-of-tolerance result, and run an impact assessment on the product the gauge accepted since its last good calibration.
- Hold when the evidence is mixed or too thin.
On the exam
CQT and CQI questions ask what data justifies changing an interval (as-found history), what to do when a gauge is found out of tolerance (shorten the interval and assess the product), and what traceability means: an unbroken chain of calibrations to national or international standards.