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An extra brief historical past of the SI prefixes

An extra brief historical past of the SI prefixes

2023-12-23 03:13:36

Along with the SI base items and SI derived items, the SI prefixes kind the idea of the worldwide system of items (SI) as we now realize it [1]. The SI prefixes permit the formation of decimal multiples and sub-multiples of the SI items. They’re handy for expressing the values of portions which are a lot bigger than or a lot smaller than the SI unit, such that the numerical worth introduced is on the ‘human scale’ (between 0.1 and 1000, and ideally between 1 and 100). This makes measurement outcomes simple to conceptualise, talk and interpret, over time, between places and throughout totally different technical disciplines.

In 1966, shortly after the twelfth Basic Convention on Weights and Measures (CGPM) had added the SI prefixes femto (for 10−15) and atto (for 10−18) to the system, De Boer revealed a brief historical past of the prefixes as much as that date [2]. In conclusion, he mirrored, ‘it could be that in future additional extension can be wanted however in the interim this doesn’t appear crucial’. In over half a century since then it has certainly proved crucial to increase the vary of SI prefixes. This text relates that progress and the reasoning behind the modifications, particularly the current replace accredited by the twenty seventh CGPM
1

, and likewise supplies a quick dialogue of potential developments in future.

2.1. 1964–2017

The interval from the twelfth CGPM in 1964 to the fifteenth CGPM in 1975 represented an uncommon interval throughout which the protection of SI prefixes was asymmetrical. (An asymmetry had beforehand existed previous to the formalisation of the SI between 1904 and 1935 when myria, for 104, was adopted however with the submultiple vary extending solely so far as milli, for 10−3.) In 1964 the necessity to signify the small dimensions occurring in nuclear physics and the requirement to measure with rising precision time intervals related to secure atomic phenomena had required extension of the vary of SI prefixes for the submultiples 10−15: femto (f); and 10−18: atto (a). Nonetheless, no comparable extension to the vary of multiples had been made. Instantly after this extension, the Worldwide Committee for Weights and Measures’ (CIPM) Consultative Committee for Items (CCU
2

: established in 1964 to exchange the Fee for the System of Items arrange by the CIPM in 1954) started contemplating an extension to increased multiples, even discussing the reintroduction of compound, or double, prefixes as a option to obtain this. In 1974 the CCU, considerably reluctantly, accepted the necessity to tackle the magnitudes then related to measurement of the frequency vary of electromagnetic radiation, world power utilization, and radioactivity when expressed in becquerels, by reviving a proposal first made on the CCU in 1971 to develop the vary of prefixes with the multiples 1015: peta (P); and 1018: exa (E). This was adopted on the fifteenth CGPM in 1975. Dialogue on prefixes continued. The CCU in 1974 had already begun to debate what names and symbols may be required for additional enlargement of the vary of SI prefixes, and on the CCU assembly in 1976 there had been proposals for solely totally different nomenclatures for expressing powers of 10 not using SI prefixes in any respect. These proposals have been consulted upon however there was no urge for food for additional change on the time.

No vital dialogue then occurred till 1990 when the CCU mentioned increasing the vary of SI prefixes to between 1024 and 10−24. On the time the argument to develop the vary within the sub-multiple route derived primarily from the magnitude of the Avogadro fixed and the necessity to categorical molecular portions in SI items whose magnitude was extra suited to molar portions. Analytical chemistry and spectroscopic methods had superior to the stage the place small fractions of an attomole (the smallest quantity that may very well be specified utilizing the then present SI prefixes) may very well be detected, particularly for macromolecules. It was additionally famous that the attojoule, aJ, and the attogram, ag, have been too massive for the aim of scientists who routinely handled single molecules. There have been no comparable arguments at the moment to increase the vary of prefixes for optimistic powers of ten as much as 1024, apart maybe from use in astronomy, nevertheless it was acknowledged that it could appear silly to increase the vary at one finish and not using a comparable extension on the different. Adapting the recommendations from the 1974 CCU assembly, the proposal was made to develop the vary to between 1024 and 10−24 utilizing for 1021: zetta (Z); for 10−21: zepto (z); for 1024: yotta (Y); and for 10−24: yocto (y). This was adopted by the nineteenth CGPM in 1991.

The CCU assembly in 1995 famous that using the jansky (10−26 W m−2 Hz−1) in radio astronomy urged the necessity for SI prefixes for 10−27 and 10−30. It’s related to later discussions to notice that this CCU assembly additionally produced a advice that, contemplating utilization in computing, the SI prefixes ought to solely be used to signify powers of ten and never powers of two. The Worldwide Electrotechnical Fee (IEC) was invited to suggest names and symbols for prefixes denoting powers of two to be used in data know-how. These have been revealed in 1999, utilizing kibi (Ki) as much as exbi (Ei) (for two10 as much as 260) representing kilobinary via to exabinary [3]. By 2005 these IEC binary prefixes have been expanded to match the vary of SI prefixes with binary counterparts, as much as yobi (Yi) for two80, representing yottabinary (however in fact just for multiples, not submultiples) [4].

Dialogue of the extension of the vary of SI prefixes continued within the CCU till 2001, once more together with consideration of using compound prefixes, at which level the committee agreed to not proceed additional with any of the recommendations. After this, the subject was not raised once more on the CCU till 2019.

2.2. 2017–2022

An extra 31 years handed between 1991 and 2022 earlier than the vary of obtainable SI prefixes was additional prolonged. This represented the longest hole between extensions of the vary since prefixes have been first adopted inside the Metre Conference in 1879.

The newest extension had its origins in late 2017 when the writer heard a BBC ‘roughly’ radio programme on naming massive numbers [5]. This contained the disturbing revelation that proposals of unofficial prefix names for describing digital storage in extra of yottabytes have been quickly gaining help and notoriety within the common scientific media. Two of the recommendations made have been brontobyte (from ‘brontosaurus’) and hellabyte (from ‘hell of an enormous quantity’). (Certainly, the Google unit converter operate was already stating ‘1 hellabyte = 1000 yottabytes’ [6].) This launched a brand new driver for extending the vary of SI prefixes: making certain unofficial names didn’t get adopted de facto. Digital storage and information science have been clearly additionally areas the place developments in science and know-how, comparable to the anticipated creation of quantum computing and the exponential improve within the dimension of the worldwide datasphere, required prefixes overlaying an expanded vary of orders of magnitude. When thought-about along with the standard and ever-present want to improve SI prefix utilization in communities the place the present vary shouldn’t be match for goal (as an illustration astronomy and particle physics) it was apparent that motion was required. It was additionally clear that the digital storage and information science neighborhood actively used SI prefixes with the non-SI items bit and byte significantly extra regularly than the IEC binary prefixes, didn’t use scientific notation (e.g. 1024 bytes), and couldn’t use phrases to explain these massive numbers (e.g. ‘septillion’ for 1024) since these have by no means been universally standardised.

It was thought-about unbalanced to not lengthen the vary downwards to 10−30, although there was no rapid requirement for this save for the ever-present need to extend using SI prefixes in communities that don’t at present use them (e.g. for changing the jansky in radio astronomy). Equally, over the last extension to the vary of SI prefixes the urgent requirement was just for an extension of submultiple prefixes, however nonetheless an extension was made to the a number of prefixes as effectively. This was prescient since had this not been completed the necessities of knowledge science would have lengthy since outstripped what was supplied by the exabyte.

The names and symbols for brand new SI prefixes trigger vital curiosity within the media. That is comprehensible, however it’s the resolution about whether or not to develop the vary which must be taken most significantly. Ultimately the selection of names shouldn’t be so crucial, though it appears crucial earlier than the selection is made. For many who use the brand new prefixes they’ll grow to be effectively used and acquainted regardless. The selection of image (and thereby the preliminary letter of the identify) is extra essential to get proper as a result of these mustn’t conflict with current utilization. A overview of current symbols for SI prefixes, SI items and generally used non-SI items demonstrated that solely two letters have been at present out there to be used within the English alphabet: ‘r’ and ‘q’. Utilizing these in reverse alphabetical order mirrored the follow in 1991 when the SI prefix vary was final prolonged. Using characters exterior the English alphabet was excluded due to the requirement for common digital replica, information switch and machine readability.

Many various mechanisms for creating prefix names have been used previously. Extra just lately these have relied (fairly tangentially) on utilizing the Latin and Greek numbers for the facility to which 1000 is raised to supply the prefix multiplier. These phrases are then suitably modified, altering the preliminary letter to match the prefix image and the ultimate letter to an ‘a’ for multiples or an ‘o’ for sub-multiples, to acquire a phrase that runs collectively acceptably with unit names when written and spoken, and doesn’t have unintended meanings in different languages. Basing the names loosely on the Greek for 9, ennea (for (103)9) and the Greek and Latin for ten, deka and decem (for (103)10) the writer proposed for 1027: ronna (R); for 10−27: ronto (r); for 1030: quetta (Q); and for 10−30: quecto (q). (Initially ‘quecca’ had been urged for 1030 however was too near a profane which means in Portuguese.)

The writer’s proposals have been consulted upon inside the scientific literature [7] and on the CCU in 2019 and 2021 [8, 9], and met with basic approval. It was additionally recognised that the proposal represented a impartial addition to the SI, which was helpful however whose use was not necessary. As such, even when the brand new SI prefixes weren’t broadly adopted, nothing can be misplaced and no disbenefit or confusion can be brought about [10]. And so it was that the twenty seventh CGPM in 2022 determined to increase the vary of obtainable SI prefixes, as proven in desk 1.

The evolution over time of the vary of prefixes adopted inside the Metre Conference since 1875 is proven in determine 1.

Determine 1. The evolution over time of the vary of prefixes adopted inside the Metre Conference since 1875. The shaded space exhibits the vary of magnitudes coated and the dotted traces point out the timing of CIPM resolution or CGPM decision leading to an enlargement to the vary, and the related assembly quantity.

Standard image
High-resolution image

2.3. 2022 onwards

The expanded vary of SI prefixes as much as 1030 should immediate an replace to IEC 80000-13 [4] to supply an identical enlargement to the vary of prefixes for binary multiples. Following previous conference these can be robi (Ri) for two90 (from ronnabinary: (210)9) and quebi (Qi) for two100 (from quettabinary: (210)10).

There’ll all the time be recommendations for brand new SI prefix names within the common science media and even within the scientific literature because it stays an space of nice fascination. As long as there isn’t any actual urgent technical want for an enlargement to the vary it’s unlikely that any of those proposals can be grow to be adopted de facto. When a real requirement for an extra enlargement to the vary of SI prefixes arises, will probably be essential to reintroduce compound prefixes since no letters within the English alphabet stay out there for brand new prefix symbols (assuming characters from different alphabets stay excluded). Compound prefixes have been used previous to the formalisation of the SI in 1960. Their reintroduction would require guidelines for utilization to be established. Options for these have already been made by the writer [11]. They may very well be fashioned fairly just by permitting solely both quetta or quecto because the second prefix for multiples or submultiples, respectively. Subsequently, for multiples this might give kiloquetta (kQ), megaquetta (MQ), gigaquetta (GQ) and many others, and for submultiples this might give milliquecto (mq), microquecto (µq), nanoquecto (nq) and many others.

It has additionally been urged by the writer that in future non-decimal prefixes may be of use in chemistry to permit small portions of elementary entities to be conveniently expressed in quantity of substance phrases fairly than as a easy rely of these entities [12].

The funding of the Nationwide Measurement System by the UK Division for Enterprise, Power & Industrial Technique is gratefully acknowledged.

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