Calibration intervals: what the ILAC-G24 / OIML D 10:2022 guide says
A calibration certificate carries a date, not an expiry: the user sets the interval. ILAC-G24 / OIML D 10, revised in 2022, explains how to choose it and how to review it.
The certificate carries a date, not an expiry
A calibration certificate states the date on which the calibration was performed, not an expiry date. It describes the instrument as it was on that day: from then on, its behavior depends on how it is used, where it is installed, on knocks, relocations and adjustments. The standard for testing and calibration laboratories, ISO/IEC 17025, in clause 7.8.4.3, keeps recommendations on the calibration interval out of the certificate, unless agreed with the customer. The interval is set by whoever uses the instrument, within their own quality management system.
There is an international reference document for that decision: ILAC-G24 / OIML D 10, "Guidelines for the determination of recalibration intervals of measuring equipment", 2022 edition.
A joint ILAC and OIML guide
The guide was written jointly by the International Laboratory Accreditation Cooperation (ILAC) and the International Organization of Legal Metrology (OIML). The 2022 edition supersedes the 2007 edition; it was approved by the International Committee of Legal Metrology in October 2022 and by ILAC in December 2022.
It is addressed to laboratories, for determining and reviewing the recalibration intervals of the equipment they use, but according to its scope it also applies to inspection and certification bodies and to other parties that use measuring equipment. The guide describes a set of methods and leaves each user responsible for choosing them according to their own needs and risk assessment, for evaluating their effectiveness and for the consequences of the choice. It also states that there is no universally applicable single best practice.
Initial choice of the interval
According to the guide, the initial decision is based mainly on a risk assessment and is made by personnel with the relevant technical competence. The factors to take into account include, but are not limited to:
For each instrument, or group of instruments, an estimate is made of the period in which it is likely to remain within the prescribed limits after a calibration.
Reviewing the interval
The guide expects the interval chosen at the start not to be the optimum one: the instrument may prove more or less reliable than expected, use and maintenance may differ from what was anticipated, and the drift found at recalibration may show that a shorter interval is needed or that a longer one is possible without increasing risk. New equipment should be calibrated more often, to identify trends in its performance early.
Review is therefore ongoing, and the guide does not recommend fixed intervals unless the interval is specified in a normative document, such as a reference procedure or a consensus standard. Five methods are described:
Method 1, staircase (calendar time)
At each calibration the next interval is extended, or kept unchanged, if the deviation from the reference value lies within a defined percentage of the range between the maximum permissible errors; otherwise it is reduced. It is easy to manage; the guide warns against reaching very long intervals with this method.
Method 2, control chart (calendar time)
A few significant calibration points are chosen and their results plotted over time, to calculate dispersion and drift and, from these, the interval. It requires good knowledge of the instrument and does not suit equipment without drift.
Method 3, in-use time
As the first two, but the interval is expressed in hours of use rather than months; it suits instruments subject to wear in use.
Method 4, in-service checking
Critical parameters are checked frequently with a dedicated device or portable equipment; a full calibration is performed when a check finds the instrument outside its limits.
Method 5, other statistical approaches
Applied to individual instruments or to groups of instruments.
Between one calibration and the next
Two recommendations of the guide apply to any method.
Intermediate checks
A system of intermediate checks ensures that the instrument works correctly between calibrations, as also provided for in ISO/IEC 17025, where needed.
Historical data
Calibration results are collected and retained as historical data, which form the basis of future decisions on the interval.
For a balance, intermediate checks are made with test weights of a class suited to the instrument. Archived certificates, placed side by side, show how the balance has behaved over time and how much it has drifted between calibrations: they are the evidence for confirming the chosen interval, or for changing it.
ILAC and IAF, a single organization since 2026
Since 1 January 2026, ILAC and IAF (International Accreditation Forum) have operated as a single organization, Global Accreditation Cooperation Incorporated (Global ACI), with a new mutual recognition arrangement that will cover the scopes of the previous ones, and a transition period. According to the IAF announcement, accreditations issued under the ILAC MRA and the IAF MLA continue to be recognized during the transition.
- ILAC-G24 / OIML D 10:2022, Guidelines for the determination of recalibration intervals of measuring equipment (PDF).
- ILAC, G series guidance documents.
- UKAS, LAB 5 Reporting calibration results, edition 5, January 2025, § 3.7: a recalibration date on the certificate only when requested by the customer.
- IAF, launch of Global ACI, 1 January 2026.
- Accredited calibration of balances and micro-dispensers: validity, interval, calibration versus adjustment, reading and checking the certificate.
- Guide to the ACCREDIA calibration certificate (PDF): the certificate explained section by section.
- Weight class and balance: the table of OIML classes by type of balance.
Gibertini Elettronica calibrates balances of any brand as LAT calibration center No. 00121, accredited by ACCREDIA.
Last updated: November 5, 2026