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Revised Guidelines on the Uncertainty of Force Measurements published

EURAMET’s mass metrology experts have prepared a publicly accessible revised edition of Calibration Guide No. 4 on uncertainty of force measurements, re-categorising force machines based on their traceability path to the International System of Units (the SI).



A wide range of industries make use of tensile or compressive force measurements in a variety of applications, from testing materials to the proof loading of bridge bearings. In all cases, the equipment used to make the measurements must be traceable to a realisation of the SI derived unit of force - the newton - within a required uncertainty.


The revised ‘Guidelines on the Uncertainty of Force Measurements’ has been developed by EURAMET’s Technical Committee for Mass and Related Quantities, and provides guidance on the estimation of force measurement uncertainty in forces generated by;

- SI reference force standard machines

- Other force standard machines

- Force-measuring instruments

- Industrial force-generating equipment


In particular, the revised edition gives the re-categorisation of force machines based on their traceability path to the SI unit of force.

Machines that derive their traceability via in situ calibrations using force transfer standards are termed Force Standard Machines (FSMs) while those which derive their traceability by any other means are termed SI-FSMs. The calibration methodology for the two types of machines is described in detail in revised Calibration Guide No. 4. This replaces the Method A and Method B calibration approaches given in the previous version. 

Further changes were incorporated to make the document more useful to the reader. These include: illustrations of different types of force standard machine, an example uncertainty budget for deadweight force standard machines, additional information on a range of uncertainty contributions, an extended list of references, and full worked examples for ISO 376 and ISO 7500-1 calibrations.


Andy Knott (NPL, UK), lead author of the revision said:

“The project started in 2017 with the aim of making the guide more user-friendly by incorporating illustrations, examples, and additional information, with input from several National Metrology Institutes. On reviewing the technical content, some possible anomalies and ambiguities were discovered, leading to a redefinition of machine types to clarify recommended calibration methodologies. These changes were incorporated just as face-to-face meetings were no longer possible, so the collaborative work was instead carried out virtually. I would like to thank all of my co-authors for their input and hope that this revision meets its objectives and proves useful to force calibration organisations worldwide.”

The ‘Guidelines on the Uncertainty of Force Measurements’ are available for download here:


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