The UK’s independent authority on slip resistance

Important update regarding Rz value to estimate slip resistance


The Rz parameter measured by the Surtronic Duo (as used in the HSE work on surface microroughness) is derived using a 2CR filter. The Surtronic Duo II uses a Gaussian filter. It is this difference in the way the data is processed that may result in a different Rz value being recorded. Spectrum have now confirmed that the 2CR filter is available and can be selected when using a Surtronic Duo II purchased Jan 2021 onwards. The selection of the 2CR filter is confirmed in the Surtronic Duo II 2021 display.

If operators measure Rz and intend to use it to complement pendulum test values (PTV) the Rz and PTV measurements must be made simultaneously and the 2CR filter must be used.

Operators should be aware that the nature of the surface of the supplied verification foil means that very similar Rz values may be recorded using either filter on this surface. As such this is not a check that the correct filter has been selected.

These notes refer to the Surtronic Duo and the Surtronic Duo II only. Operators must check with the instrument manufacturer if using any other meter.

The results spreadsheet is available in the members’ area.

If you would like to learn more about this work please contact the Secretary.


A presentation considering surface microroughness data was given at the Group meeting on 6th June 2019. The data presented suggest that 2 different machines, which appear to be measuring the same microroughness parameter, can give different results. The way the measured data is filtered appears to be the reason for the observed differences.

The Group reminds members, and other interested parties, that the roughness measurement should be considered as a complementary measurement to be used in conjunction with pendulum test values. Section 7 of the current Guidelines refers (Issue – 5 October 2016). Data from a single meter should only be used alongside PTV data generated at the same time in similar areas of the same flooring material. This may allow the experienced operator to make a comparison. As part of the ongoing review of the Guidelines the sections covering microroughness will be updated.

Share this:

Become a member and get involved in the UK Slip Resistance Group