A workshop check records how an instrument read known blocks today. A manufacturer inspection sheet is the maker’s outgoing test. A UKAS certificate is a report from an accredited laboratory, with a stated uncertainty and a defined object. Calling a shop check “calibrated” or “UKAS” without that certificate overstates the evidence.
Three documents, three jobs
| Document | Who issues it | What it can support |
|---|---|---|
| Workshop check record | The shop that used the instrument | Observed differences and scatter on named blocks, at a recorded temperature and contact method. |
| Manufacturer inspection | The maker or its outgoing test bench | That a unit was checked to the maker’s own procedure before despatch. It is not a UKAS certificate. |
| UKAS certificate | A laboratory accredited for that measurement | A defined object, date, method, uncertainty and traceability statement. NPL’s own gauge-block service page is an example of that class of work, not a shop blog result. |
NPL GPG 40 is a use guide. It tells you how force, dirt and temperature affect callipers and micrometers. It does not convert a shop notebook into an accredited certificate.
What “calibrated” would have to show
On this site, the word calibrated is reserved for a certificate that identifies the object, the date, the reference artefacts, the uncertainty and whether the laboratory is UKAS accredited for that work. A photograph of a grade label or a certificate number on a gauge block can support the reference side of a shop check. It does not, by itself, calibrate the micrometer or caliper.
NPL’s gauge-block service page quotes laboratory uncertainties for that service, including an interferometric central-length example for 0.5–100 mm. Those figures belong to that laboratory. They are not a workshop capability and they are not copied here as a shop target.
Machinist Guides’ 4:1 ratio, taken from MIL-STD-45662, is a US document habit about how much better the reference should be than the instrument. It is cited as that source’s rule, not as a UK statutory requirement.
What a shop record should still contain
Even when the document is only a workshop check, the record is stronger if it keeps:
- block identity, nominal size in millimetres, and grade or certificate number;
- whether any stack was wrung, and of which materials;
- temperature;
- contact method;
- repeats and their range;
- a clear sentence that the sheet is a shop check, not a UKAS certificate.
MeasureProof has not photographed a gauge-block certificate for a published test, and has not issued a calibration certificate. This page explains the distinction. It does not treat a related retail listing as a calibration by this publication.
Sources and scope
Sources checked on 23 September 2026. Numbered references point to the original publishers. Their sample measurements are not MeasureProof measurements. Manufacturer and forum material is identified separately.
- NPL Good Practice Guide 40, Callipers and micrometers ↗National Physical Laboratory. UK authority for use conditions, measuring force and temperature. It is not a workshop certificate.
- NPL gauge-block and length-bar calibration ↗Laboratory service page. Quoted uncertainties belong to that service (UKAS 0478), not to a shop check.
- Machinist Guides, Ultimate guide to micrometer calibration ↗Page dates: 18 April 2021 published, 1 March 2026 updated. Cites a 4:1 ratio from MIL-STD-45662. That is a US document, not a UK workshop statute.
No instrument in this note has been tested or certified by this publication. Evidence policy · Corrections
Keep the conditions with the reading.
The CSV has column headings and one empty row. It contains no fabricated sample readings.
Download workshop-check record ↓
