Calibration is the process of comparing the readings of a measuring instrument with a reference standard of known accuracy, recording the difference, and adjusting the instrument if the difference is larger than allowed. In plain terms: can we trust what this device tells us?
"Calibration work" usually means the whole job: testing a gauge, scale, wrench or medical device across its range, adjusting it if needed and returning it with a certificate. It is not the same as repair, and a repaired instrument usually needs calibrating before it goes back into use.
How calibration works
- Define the requirement. Each device gets an ID, a range and a tolerance (the maximum error accepted), for example ±0.5 °C.
- Choose a reference standard more accurate than the instrument under test; 4:1 or better is a common rule of thumb.
- Record the as-found readings. Test at several points before touching anything, to show whether it was in tolerance while in use.
- Adjust if readings are outside tolerance or close to the limit.
- Record the as-left readings to prove it now meets tolerance.
- Issue the certificate and label. The certificate records readings, the standard and its traceability, uncertainty, technician and date; the label shows the next due date.
- Set the next due date from the calibration interval on the maintenance schedule and return the instrument to service.
Traceability, tolerance and intervals
| Concept | What it means | Why it matters |
|---|---|---|
| Traceability | An unbroken, documented chain of calibrations linking your reference standard to national or international measurement standards | Lets an auditor trust that your 1 kg mass really is 1 kg |
| Tolerance | The maximum error allowed for the instrument’s intended use | Decides pass or fail |
| Measurement uncertainty | The doubt in the calibration result itself | A reading just inside tolerance may not be a safe pass if uncertainty is large |
| As-found / as-left | Readings before and after adjustment | As-found shows whether past work is at risk |
| Calibration interval | Time or use between calibrations | Too long risks bad measurements; too short wastes money |
Quality standards set expectations rather than fixed intervals. ISO 9001 (clause 7.1.5) expects measuring equipment to be calibrated or verified at specified intervals against traceable standards, with records, and action when it is found out of tolerance. ISO/IEC 17025 sets requirements for the competence of testing and calibration laboratories; using an accredited lab is a common way to show traceability.
Calibration examples by industry
- Hospitals: infusion pumps, patient monitors and defibrillators checked by biomedical engineering on a planned cycle. See asset management for healthcare.
- Manufacturing: torque wrenches, micrometers and pressure gauges, where one out-of-tolerance tool puts every part measured since its last good calibration in doubt. See asset management for manufacturing.
- Laboratories: analytical balances and pipettes checked against certified masses and volumes.
- Mining, oil and gas: portable gas detectors bump-tested before use and calibrated with certified test gas.
Common mistakes
- Recording only "pass". Without as-found readings you cannot tell whether past work was affected.
- No out-of-tolerance procedure. Decide in advance who reviews the impact and how far back to look.
- Fixed intervals forever. Lengthen intervals for instruments that always stay well within tolerance; shorten them for ones that drift.
- Losing the instrument. A due date is useless if nobody can find the gauge. Give it an asset tag and record its location.
Spreadsheet vs calibration software
A small lab can run calibration from a spreadsheet: one row per instrument with ID, location, interval, last calibration, next due (=EDATE(last_cal, 12)), result and certificate number. It breaks down as the list grows: nobody filters the sheet weekly, certificates live elsewhere, and each new result overwrites the last, so there is no history. Calibration software ties the schedule, job, result and certificate to the instrument.
Calibration in Asetavo
In Asetavo maintenance (Business plan), you set up a calibration schedule for one instrument or a whole category, every N days, weeks or months. Instruments coming due appear on the Due & overdue list, and a planner generates a calibration work order. Completing it writes a calibration record with the result (pass, fail or adjusted), the standard used, the certificate reference, the technician and the next due date; records can also be entered directly. Scanning the instrument's QR, barcode, NFC or RFID tag brings up its history.
