Recently on a Windows Phone project I got a bug raised that I was formatting the currency for South Africa incorrectly (in particular the use of a comma to separate the Rands & cents – i.e. the decimal mark) which sparked off an investigation into what is the correct way to format the currency in the country I live in.
tl;dr: The comma is the decimal mark for South Africa.
As I am a developer my first stops were Microsoft & IBM who both have guides on this that states the decimal mark for South Africa is a comma. Wikipedia also states that officially the comma is has been adopted as the decimal mark.
Not happy with that vague “official” - I dug further to try and find a more official source which lead me the University of Johannesburg (UJ) style guide, which is meant to assist students with the correct language style to use in their documents. The very interesting bit is in section 6 (bold & underline added by me):
Note the spaces and commas in the following: 3 000 (or 3000); 3 500; 2 354 701; R5,87. The so-called Continental System (also used in South Africa) requires that the decimal point be replaced by a comma. However, it is not always possible to do this, since many computer programs require a decimal point for calculations.
So UJ agrees with the usage of the comma – but for me this also gave me a clue to find more info in something called the Continental System… which didn’t lead anywhere.
I then happened to find the 2012 Winter School textbox for Grade 10 Maths Literacy which also states:
South Africa officially uses a decimal comma, with a space as thousands separators.
1 450 789,32 = one million; four hundred thousand; fifty thousand; zero thousands; seven hundreds; eighty; nine; three tenths; two hundredths.
Finally I found some official documentation on the subject, first up Government Editorial Style Guide which states – still not saying it is “official” as Wikipedia said:
Write decimal and negative numbers as numerals: 3,3 and –4. Use the decimal comma, not the decimal point: 17,4 million.
Use a space, not commas, to indicate thousands: 3 000, 20 000.
However the best source I found was a document titled The South African measurement system and its origin by EE Publishers which has the following:
Finally, it is worth noting that, in Table 1, the grouping of thousands (in threes) and the use of the decimal comma, as opposed to the decimal point, was effected, to be in accordance with the applicable legislation of South Africa: “where the magnitude of a quantity is expressed in terms of a unit, a comma on the line is used as the decimal sign in the numerical part of the expression and the digits are separated into groups of three digits on either side of the comma by means of spaces…” . The exception was made, for land registration purposes, by the then Director-General of Surveys, who judged, in his Circular No. 2 of 1971: “it has been decided to abandon the writing of areas, such as 45 236 1 ha with a space after the 3rd decimal figure and to advocate that as in the past the four figures be grouped together viz. 45 2361 ha”. Here, a space was left between the number and the symbol of a unit, as required . These rules were highlighted in an old Land Survey Act No. 9 of 1927 (Regulation 24.1), but an amended Land Survey Act No. 8 of 1997 does not contain such information.
English-speaking countries (plus China, India and Japan) use the decimal point. There seems to be a general tendency to formally declare its use worldwide and the International Organisation for Standardization, ISO, also tends towards using the decimal point over the decimal comma. In view
of the South African law, however, the comma shall still be employed in South Africa as “the only recognised decimal indicator for all numbers” .
 DR Hendrikz: South African Units of Length and Area, Department of Lands, Trigonometrical Survey, Special Publication No. 2, 1944.
 Measuring Units and National Measuring Standards Act, 1973 (Act No. 76 of 1973), Government Gazette No. 4326, 5 July 1974.
 The International Metric System (SI), Guide to the use of the SI in South Africa, The Council of the South African Bureau of Standards, M 33a, 1992
 Measurement Units and Measurement Standards Act, 2006 (Act No. 18 of 2006), Government Gazette No. 29752, 28 March 2007.
 T Zakiewicz: “Units of Length Measure & Geodetic Standards at the Cape, 1813-1912”, History of Surveying and Land Tenure, Collected Papers,
Vol. 2, The Institute of Professional Land Surveyors & Geomaticians of the Western Cape, May 2004.
WOW! That gives the official acts and a great depth of knowledge into the subject matter and for me answers it once and for all – we use a comma!
The two final locations I found in my searches provided some interesting information on the comma as a decimal mark in general (i.e. not specific to South Africa). First up is the Wikipedia page for International System of Units which states
The 10th resolution of CGPM in 2003 declared that "the symbol for the decimal marker shall be either the point on the line or the comma on the line." In practice, the decimal point is used in English-speaking countries and most of Asia, and the comma in most of Latin America and in continental European languages.
Secondly is a forum answer about the use of the comma:
Sender: Franck Menuge
Subject: comma as decimal separator
Could somebody tell me the origin of the use of a 'comma' as a decimal separator and of a 'dot' for thousands in the French numeric system, ex.1.234,56 Is it only used in France or in other european coutries? Why is it different in the UK?
The comma as a decimal separator is used in several continental European countries, including Germany, Austria, Switzerland, Belgium, Luxembourg, and - we think - also Italy and the Netherlands.
The notational convention of using a punctuation mark to separate the fractional part of a number seems to have begun with John Napier,a Scot, in his book "Descriptio" published in 1616. In this book he proposed using a decimal point (period) to separate the whole number part from the decimal part of a number. In the following year, 1617, in his book "Rhabdologia" he proposed a point or a comma as the decimal sepatatrix. In his writing he used both. To quote Cajori, "Napier vacillated between period and comma; mathematicians have been vacillating in this matter ever since", Florin Cajori, "A History of Mathematical Notation", 1974 page 324. By 1619 the decimal point had become standard in England.
In Earliest Uses of Mathematical Symbols under Grouping the claim is made that the modern system of separating a numeral into groups of 3 with commas first appeared in 1795 in the article "Numeration" in "Mathematical and Philosophical Dictionary" by Hutton. Again the reference is from Cajori.
The confusion doesn't stop there. In the school system in North Amarica teachers have started to use a space rather than a comma to separate the digits in a numeral into groups of three. Thus the number thirty-one thousand three hundred twenty four and six tenths is written 31 324.6. One last point. Notice that the decimal point in the number 31 324.6 in on the line were it is our understanding that in the UK you would write this number with the decimal point floating above the line. In North America the period floating above the line indicates multiplication, so
Patrick and Penny