
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?
Many thanks,
Hi Frank,
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 thirtyone 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
Cheers,
Patrick and Penny
