Comment on Dimensionless Units in the SI

TL;DR

This paper critiques recent proposals on SI units related to angles, hertz, and countable quantities, and offers clearer, less problematic alternatives to improve consistency and clarity in SI unit usage.

Contribution

It proposes specific revisions to SI guidelines, including clarifying angle measurement, restricting hertz usage, and promoting the presentation of countable quantities as pure numbers.

Findings

Clarifies the SI brochure's text on angles.

Recommends relegating hertz to a non-SI unit for specific cases.

Encourages describing countable quantities with accompanying text.

Abstract

The recent paper by Mohr and Phillips (arXiv:1409.2794) describes several problems relating to the treatment of angle measurement within SI, the unit hertz, and quantities that can be considered countable (rather than measureable). However, the proposals that they put forward bring new problems of their own. This paper proposes alternative suggestions that solve the problems less painfully. Specifically, clarifying the text on angle in the SI brochure; relegating the hertz to a "Non-SI unit accepted for use with the International System of Units", with specific application only for "revolutions or cycles per second"; and encouraging countable quantities to be presented as pure numbers, while requiring that a sufficient description of the quantity being counted is given in the accompanying text.