Calibration and traceability: building a laboratory record that survives an audit

By Vvon Engineering Team | Published 2026-07-15 | Updated 2026-09-13

What a calibration certificate must actually contain, how to read an accreditation scope, how to set your own intervals and defend them, and the intermediate checks that catch drift between calibrations.

Scientific & laboratory RFQ checklist (TXT)

A defensible calibration programme needs more than certificates: suitable measurement uncertainty, justified intervals and intermediate checks help determine whether equipment remains fit for use. Review these together with the method’s tolerances and the consequence of an incorrect result.

What a calibration certificate has to say

A calibration certificate is a measurement report. If it does not report measurements, it is a service visit record with a border printed on it. Check every certificate you receive against this list, and reject the ones that fail.

• Unambiguous identification of the item: manufacturer, model, serial number and your own asset identifier. 'Balance, Laboratory 3' identifies nothing.
• The reference standards used, with their own identification and their own traceability. This is the link in the chain, and it is the line most often missing.
• Results and uncertainty. Record the uncertainty and its stated coverage information. A conformity decision also needs the specification and an agreed decision rule; a numerical result alone does not settle a borderline pass or fail.
• As-found and as-left results where applicable. Request pre-adjustment results to assess past use. Post-adjustment results describe the condition after work; neither proves how the instrument performed on every previous day.
• The environmental conditions and the method under which the calibration was performed, because a temperature-sensitive measurement made in different conditions is a different measurement.
• The date, the person and the laboratory, plus the accreditation mark and reference number where the calibration is accredited.
• Any statement of conformity, and the decision rule behind it. If the certificate says 'pass' on a result sitting close to the tolerance limit, it has to say how uncertainty was handled in reaching that verdict.

A related trap at purchase: a manufacturer's factory test report is not the same as a calibration certificate, even when it carries impressive figures. It typically demonstrates that the instrument met the manufacturer's specification on the production line, without traceable reference standards named, without uncertainties, and without an accreditation scope behind it. Ask which one you are being offered before the equipment ships.

Traceability is a chain, and you are entitled to see it

Metrological traceability relates a measurement result to a stated reference through a documented, unbroken chain of calibrations, each contributing to uncertainty. SI traceability should be used where technically possible; some measurements rely on another appropriate reference, such as a certified reference material or reference procedure. The JCGM vocabulary and uncertainty guides define these concepts.

In Bangladesh the practical landmarks are the national metrology laboratory maintained under BSTI, and the Bangladesh Accreditation Board as the national accreditation body. The point that saves the most trouble: an accredited laboratory has a scope document listing exactly which quantities, ranges and uncertainties its accreditation covers. Read the scope, not the logo on the letterhead. A laboratory accredited for mass is not thereby accredited for temperature, and if the parameter you need is outside the scope then the certificate you receive is an ordinary commercial calibration, whatever badge is printed on it.

Where local coverage is unavailable, examine an overseas provider’s current accreditation scope and the applicable recognition arrangement. Confirm that the range, uncertainty, method and certificate meet your laboratory’s and customer’s requirements; a foreign accreditation logo does not automatically make every service acceptable.

Setting the interval yourself, and defending it

The calibration interval is a risk decision that belongs to the laboratory, not a number the manufacturer hands down. Auditors rarely object to an unusual interval. They object to an interval nobody can explain. Base yours on five inputs: the manufacturer's recommendation as a starting point, the drift you have actually recorded at previous calibrations, how heavily the instrument is used, the consequence of reporting a wrong result from it, and the environment it lives in.

Review as-found drift and intermediate-check history alongside use, environmental changes and transport. An interval may be shortened or extended where the evidence and applicable requirements support it. Document the review and preserve any mandatory manufacturer, method or regulatory constraints.

Instrument	Potential change	Example check to adapt to the method and risk
Analytical balance	Sensitivity and corner load, aggravated by vibration, draughts and an unstable bench	A suitable check with a class weight at working load; repeatability and eccentric-load checks where required
pH meter	Electrode slope and offset; electrodes age quickly in warm storage	Two-point buffer calibration before each session, with the slope recorded and trended rather than merely accepted
Air displacement pipette	Piston and seal wear, worse with aggressive or volatile reagents	Gravimetric check on a calibrated balance at method-appropriate volumes, with results plotted
Incubator, oven, refrigerator, freezer	Controller sensor drift, and a spatial gradient the fixed sensor never sees	Independent logger placed at the worst location found during mapping, reviewed on an approved interval against minimum and maximum
Autoclave	Chamber temperature against gauge reading, drain and trap blockage	Independent data logger in a representative load, plus the indicator policy your discipline requires
Pressure gauge or flowmeter on a gas line	Mechanical drift and internal corrosion in humid air	Comparison against a calibrated reference gauge on a written interval
Fixed and portable gas detectors	Loss of sensor sensitivity, and poisoning that leaves no visible trace	Bump test to the written policy; span calibration at the set interval
Timers, thermometers and hygrometers	Slow drift that nobody notices because nobody looks	Scheduled comparison against a calibrated reference kept solely for that purpose

Intermediate checks: the part that actually protects results

Intermediate checks provide evidence about selected aspects of performance between calibrations. If an instrument is found out of tolerance, assess affected results using the failure mode, trend, check coverage and last defensible evidence of acceptable performance. The last passing check does not automatically rule out every earlier error.

• Choose a fit-for-purpose check item. It must be sufficiently stable for the characteristic being monitored. A certified value or traceability is required where the check or method depends on it; an unassigned stable item can monitor repeatability without proving accuracy.
• Plot the results on a control chart with warning and action limits derived from your own scatter, not copied from a textbook. A number in a logbook is data; a chart is information, and the trend appears on a chart weeks before it breaches a limit.
• Attach the check to an existing routine. A check that requires someone to remember it, find the standard and open a separate record will not survive a busy month. A two-minute check at the start of a run will.
• Cross-check against a second instrument where you have one, and against a second operator periodically, which catches technique drift as well as instrument drift.
• Record failures as well as passes. Investigate unusual trends and preserve corrective actions. A clean record alone is not proof either of good performance or of dishonest checking.

Building the record

1. Maintain an equipment register with a unique identifier for every item, physically labelled on the item itself and not only present in a spreadsheet. Include receipt date, location, status, and the person responsible.
2. Keep one calendar of calibration due dates, owned by one named person. Distributed responsibility means no responsibility, and the item that gets missed is always the one on the boundary between two departments.
3. Label each instrument with its calibration status: last date, due date, and any restriction on use. Anyone picking the instrument up should not have to open a file to know whether they may use it.
4. Write an out-of-tolerance procedure before you need it. It has to answer the difficult question: what do we do about the results we have already reported? That means defining how far back to look, how to assess the impact, who decides whether customers or clinicians are notified, and how the decision is recorded. This is the procedure auditors probe hardest and the one most laboratories have never written.
5. Define your decision rule for statements of conformity, so that pass and fail verdicts near a limit are made consistently and the treatment of measurement uncertainty is documented rather than improvised.
6. Quarantine and label failed equipment immediately, physically removing it from service. An instrument marked out of service but still sitting on the bench will be used.
7. Retain certificates for the period your quality system requires, indexed so that any certificate can be produced in under a minute. The speed with which you can produce a document changes how the rest of the audit goes.

Buy calibration with the equipment, not after it

State the calibration and verification deliverables at procurement so that the laboratory can assess the provider, scope and installation effects before accepting the instrument.

• Specify the calibration needed for the intended use. Where accredited calibration is required, agree the scope and provider. Some measurements must be performed after installation; distinguish factory calibration from site verification and commissioning.
• The first scheduled recalibration inside the contract, with a named provider and a named date, so the first renewal is not an unbudgeted purchase.
• The reference items needed for your own intermediate checks: class weights, buffer solutions, a reference thermometer, a reference gauge. These are inexpensive against the instrument and impossible to obtain quickly once the audit is scheduled.
• The manufacturer's site preparation document supplied before civil works begin, which sets the environmental and supply conditions the calibration will assume.

Record when calibration was performed and assess transit, storage and installation effects before use. Establish the first recalibration due date through the approved interval policy; the warranty start and installation date are not automatic substitutes for a calibration assessment. ILAC guidance includes decision rules and calibration-interval review.

Have a project to scope?

Share your application, equipment requirements and procurement timeline. Our engineers can help clarify the configuration and scope for your enquiry.

Discuss your requirements

Browse buying and selection guides | Back to all Insights