National Physical Laboratory

Step gauges

Step Gauge

A UKAS accredited calibration service for step gauges.

Key features

  • UKAS accredited
  • Two week turnaround time
  • Calibration of various styles of gauge
  • Temperature tightly controlled
  • Length and parallelism measured
  • Calibration and measurement capability: (0.1 + 0.000 236L) micrometres (where L is the length in millimetres)

Mechanical reference artefacts such as step gauges provide a cheap and effective way of assessing the performance of a Coordinate Measuring Machine (CMM) for a length measuring task. Step gauges are particularly well suited for performing formal performance verification procedures described in national or international standard specifications, such as BS EN ISO 10360-2:2009 - Geometrical product specifications (GPS). Acceptance and reverification tests for coordinate measuring machines (CMM). CMMs used for measuring linear dimensions.

The introduction of the BS EN ISO 14253-1:1999 decision rules has implications for users choosing suitable reference artefacts for CMM verification because it gives explicit guidance on the 'pass/fail' criteria. These criteria take into account the uncertainty of the verification process, which in turn depends on both the uncertainty in the calibration of the reference artefact and on the control of the machine's working environment. As a high uncertainty associated with the reference artefact reduces the conformance zone assigned to the CMM, it is desirable to have the best possible calibration of the artefact.

Housed in a state-of-the-art close controlled room, NPL has developed a semi-automated step gauge calibration system which uses laser interferometry to achieve the smallest uncertainty for calibration of step gauges in the UK. Step gauges up to 1500 mm long can be calibrated.

We have extensive experience of calibrating standard designs by manufacturers, including:

  • Mitutoyo (Check Master and High-Accuracy Checkmaster)
  • KOBA (KobaStep)
  • TESA
  • Starrett

Custom designs can also be accommodated, please contact us to discuss your requirements.


Measurements are made on the central length and face parallelism. The UKAS calibration certificate states the distance between the centre of the faces and highlights any faces where the parallelism measurements show cause for concern.

Calibration and measurement capability

Calibration and measurement capability (CMC) expressed as an expanded uncertainty (k = 2) for a particular step gauge depends on the length of the gauge and its overall quality of manufacture. Typically, a 1 m step gauge can be calibrated with an expanded uncertainty of 0.34 µm.

The CMC expressed as an expanded uncertainty (k=2) is given by the equation:

(100 + 232L) nanometres, where (L is the length in metres)

Turnaround time

We aim to turn around a single step gauge within two weeks but often gauges are turned around well within this timeframe.


GPG(042): CMM Verification (Issue 2)


Customer Service tel: 020 8943 8631

Last Updated: 14 Jul 2016
Created: 31 May 2007


Please note that the information will not be divulged to third parties, or used without your permission