The latest iteration of the International System of Units has been a long time coming, explains Richard Brown, and it’s necessary if we are to keep up with developments in science.
November 18 2022 marked the first update to the list of International System of Units (SI) prefixes since 1991, an event that has been five years in the making.
SI is the world’s system of measurements units and within it lie three pillars: the SI base units, the SI derived units and SI prefixes. Not only do prefixes permeate our everyday weights and measures – for example the kilogram, centimetre and millilitre – but they also appear in technical terms we all use such as nanotechnology, micro-scooter and Gigafactory.
Prefixes make it easier to express large measurements, for example, we might refer to 1 kilometre instead of 1,000 metres. Over the years our system of SI prefixes has expanded in response to advances in science and technology requiring access to an increased range of orders of magnitude relating to measurement.
This most recent update has been driven by the requirements of data science, digital storage and the exponentially growing size of the global datasphere, which is already beginning to use prefixes at the top of the scale prior to this update. In 2017, I was listening to a BBC More or Less podcast when I first came across the issue of unofficial names for ‘1027 bytes’ being widely used, with the danger of these being adopted de facto.
Our system of SI prefixes has expanded in response to advances in science and technology requiring access to an increased range of orders of magnitude
These were brontobyte (from ‘brontosaurus’) and hellabyte (from ‘hell of a big number’). Not only would that be confusing as ‘B’ and ‘H’ are already in use as symbols for well-known prefixes and units, but also, they are unsystematic compared to the names of other prefixes.
As the Head of Metrology at the NPL, the UK’s National Metrology Institute, I knew the SI had to act and therefore I started the process of proposing new names for an extension to the SI prefix range – ronna (R) and quetta (Q) – as SI prefixes for 1027 and 1030, respectively, together with their microscopic counterparts: ronto (r) for 10-27, and quecto (q) for 10-30.
Not only has this update alleviated the risk of unofficial names catching on, but the new prefixes should also future proof the system for the next 25 years.
Dr Richard Brown is Head of Metrology at the National Physical Laboratory
- For more information on the redefinition of SI units and the expansion of SI prefixes, go to npl.co.uk/si-units
