Calibration interval: what the standards ask, and what they leave to you
None of the standards here gives an interval for any instrument. They ask for calibration or verification at set intervals or before use, and for the organization to set, record and review those intervals. The finder reads the interval in your register and adds it to the last calibration date; it never sets or suggests one.
What the standards say
- ISO 9001 7.1.5: calibration or verification at specified intervals, or prior to use, where traceability is required or judged essential.
- AS9100D 7.1.5: the register shows the method, frequency and acceptance criteria of each calibration or verification, and a recall process calls equipment in.
- ISO/IEC 17025 6.4: a calibration programme, set up and reviewed, and a next due date in each equipment record.
- ISO 13485 7.6: calibration or verification at specified intervals or before use, to documented procedures.
- 21 CFR 211.68 and 58.63: routine calibration according to a written program or written standard operating procedures.
Named, not quoted
ILAC-G24 / OIML D10 give guidance on setting and reviewing calibration intervals from the history of each instrument (as-found results, drift, use). ISO 10012 sets out a measurement management system. Both are named here and not stated.
How the finder reads an interval
An interval reads as months (12 months, 12M, 12 mo, 1 yr, annual, 2 years, biennial, 6 mo, semi-annual, quarterly, monthly), weeks (4 weeks, 2 wk, weekly) or days (365 d, 90 days, daily). Calendar months are added as months: 31 January plus one month is the last day of February. "Before use" is read as verification before each use, with no due date to work out. Anything else is shown as not read, never guessed.
| Pasted | Read as | Last calibration 31/01/2026 gives |
|---|---|---|
| 12 months, 12M, 1 yr, annual | 12 months | 31/01/2027 |
| 6 mo, 6M, semi-annual | 6 months | 31/07/2026 |
| quarterly | 3 months | 30/04/2026 |
| 1 month, monthly | 1 month | 28/02/2026 |
| 90 days | 90 days | 01/05/2026 |
| 2 years, biennial | 24 months | 31/01/2028 |
| before each use | no due date | none |
| biannual | not read: twice a year or every two years? | none |
Where an interval shows up in the findings
- Finding 3: no interval, or one the finder cannot read, means no due date can be worked out.
- Finding 11: the register's own due date disagrees with the last calibration plus the interval.
- Finding 4: after an out-of-tolerance reading, the interval sets the start of the period in question.
AS9100D 7.1.5Monitoring and measuring resourcesThe resources needed for monitoring and measurement to give valid, reliable results are identified and provided; they are suitable for the task and kept in good order, and records show they are fit for purpose. 9100 adds a process for calling in monitoring and measuring equipment that needs calibration or verification, and a register of such equipment showing its type, unique identity, location, and the method, frequency and acceptance criteria for calibration or verification; the register covers test hardware and test software, automated test equipment, plotters that produce verification data, and equipment owned by employees or supplied by customers. Where traceability of measurement is required, or the organization regards it as essential, equipment is calibrated or verified at set intervals against standards traceable to international or national standards (with the basis recorded where none exists), marked to show its status, and protected against adjustment, damage or deterioration. Under 9100, calibration and verification take place in suitable environmental conditions. If equipment is found to be unfit, the organization establishes whether earlier results were compromised and acts accordingly.