Obituary - Anders J. Thor, a universal linguist

Anders J. Thor, leading figure in the standardization of quantities and units and Chairman of IEC TC 25 dies

By Zoë Smart

The IEC was saddened by the death of Anders J. Thor who passed away on 7 April 2012. At the time of his death Thor was Chairman of IEC TC (Technical Committee) 25: Quantities and units, a position he had held since 1988. He also contributed as an expert to several other IEC committees.

Anders J. Thor

A lifelong goal

As a young student at the Royal Institute of Technology in Stockholm, Thor was frustrated by the various departments of the Institute using different notations for the same quantity and vowed to standardize them. He got the opportunity to do so when a public enquiry about standards was launched and he was tasked with replying on behalf of the Institute. In 1975 he was asked to take on the Secretariat of the Swedish National Committee on Quantities and Units and so his career in standardization began.

In 1978 Thor and Erik Rudberg put forward a proposal that the radian and steradian be considered derived units – rather than base units – of the SI (International System of Units). In 1980 the proposal was adopted by the CIPM (Comité International des Poids et Mesures) but it took another 15 years before the CGPM (Conférence Générale des Poids et Mesures) confirmed the decision in 1995. As Thor himself put it “Metrication, of which SI is only the top, has gone on for 200 years and it is still going forward. Therefore it doesn’t really matter if it is this year or next year, but only that you go in the right direction”.

A truly universal standard

When Thor took over the Secretariat of ISO TC 12: Quantities and Units, in 1982, IEC and ISO(International Organization for Standardization) had diverging views on the subject of logarithmic quantities and units, with IEC favouring decimal logarithms and ISO natural logarithms. But soon after taking up his new position, the then Chairwoman of IEC TC 25 Erna Hamburger invited Thor as an observer to TC 25’s working group, and he reciprocated by inviting her to become a member of TC 12’s Advisory Panel. A close relationship between the two TCs was thus established and when their respective standards were revised a number of basic principles were accepted by both. When Hamburger passed away in 1988, Thor was asked to become Chairman of TC 25 and as a result the two TCs have worked closely ever since. The German NC (National Committee) proposed that the IEC and ISO standards be harmonized and in 2009 Part 1 of the ISO/IEC 80000 family of standards was completed. It brings together the IEC 60027 and ISO 31 series under a double logo and is a style guide for the use of physical quantities and units of measurement in scientific and educational documents worldwide.

Bridging linguistic barriers

Thor once pointed out that mathematical signs and signals, the SI, symbols for chemical elements and musical notes are the four alphabets that bridge all linguistic barriers. Through his involvement in the ISO/IEC 80000 series he contributed directly to the standardization of the first three and will be remembered for his relentless commitment to standardizing systems of quantities and units based, as he put it, “on mathematically sound principles”.

Of kibis and mebis


In a TC Newsletter published in February 1999 (see below), Thor introduced amendment 2 to IEC 60027-2, an International Standard prepared by IEC TC 25 to distinguish prefixes for binary multiples from the SI prefixes for decimal multiples. The new prefixes would be of particular use in the field of information technology.

In 2005, two further prefixes zebi [(210)7] and yobi [(210)8] were added. With the amount of data produced on a constant rise and ever more powerful computers built to deal with it, there may well soon be a need for TC 25 to begin work on coining a term for the next higher magnitude.

IEC standardizes prefixes for binary multiples - Amendment 2 to IEC 60027-2

By Anders J. Thor, Chairman IEC TC 25 

Because of the near equivalence of 103 and 210 the SI (International System) prefixes kilo (k), mega (M), giga (G) etc. are often used in information and computer technology to denote powers of two, for example kilo: 210 = 1 024 and mega: 220 = 1 048 576. However, the SI prefixes are defined to denote exact powers of ten, i.e. kilo: 103 = 1 000 and mega: 106 = 1 000 000, etc. and the popular use of k. M and G introduces an appreciable inaccuracy. The relative error increases for prefixes denoting higher powers. Often these errors do not matter, but in scientific texts it is necessary to be more accurate. Therefore IEC TC 25: Quantities, units, and their letter symbols, has prepared an International Standard for prefixes for binary multiples to be distinguished from the SI prefixes for decimal multiples. These new prefixes are:


Factor Name Symbol
(210)1 kibi Ki
(210)2 mebi Mi
(210)3 gibi Gi
(210)4 tebi Ti
(210)5 pebi Pi
(210)6 exbi Ei

Thus the names and the symbols of the new prefixes are related to the old prefixes in a simple way and should therefore be easy to remember and to use. Of course, the new prefixes may also be useful outside the field of information technology.

Anders_J_Thor Anders J. Thor
fam-5_maths_lrg Thor believed mathematical signs were one of four alphabets capable of bridging linguistic barriers
kg_etalon_sevres The original Platinum-Iridium cylinder used as the standard for the kilogram is kept under glass at the BIPM