Comment on ‘On the dimension of angles and their units’

Abstract

Abstract The paper by Mohr et al (2022 Metrologia 59 053001) makes a strong case for angles having their own dimension, so that the radian should be treated as independent of the existing SI base units, and not somehow equivalent to the number 1. The authors also show how current practice effectively simplifies complete (unit-independent) equations by setting the term Θ/2π equal to 1, where Θ is the angle of one revolution, and this is analogous to how theoretical physicists sometimes set the speed of light c equal to 1. However, they make a significant error in their treatment of frequency, which needs to be highlighted. They have, in effect, adopted the standard definition for ‘angular frequency’ as their definition of ‘frequency’. This leads to unnecessary confusion and problems that are entirely separable from the issue of angles having their own dimension.