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The US and the UK uses a baseline dot as the decimal mark. Most other European countries use the comma. Here is a short piece on the history of this matter.

My question is: When did the use of the comma as the decimal mark become (largely) extinct in the US? I ask because I happened to come across this 1868 document (Maine Supreme Court ruling) where the comma was used, suggesting that it was still in some regular use in the US as late as 1868.

  • http://www.councilscienceeditors.org/wp-content/uploads/v31n2p042-043.pdf seems to imply the dot was always the most common notation in the US. Maine being a catholic, continental-European state, it is possible the European conventions dominated there (both Dutch and Italians use comas) – VicAche May 17 '15 at 15:02
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    The original decimal notation used dot. So the correct question would be "how and why the dot was replaced by comma in Europe?". – Alexandre Eremenko May 18 '15 at 05:05
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    @AlexandreEremenko I have to disagree with that. The origal decimal notation is under/overlining – VicAche May 19 '15 at 13:11
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    @AlexandreEremenko and to my knowledge, the dot "on the line" used for decimal notation in the US was never used elswhere before. – VicAche May 19 '15 at 13:12

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Lets look to some old $10,000 bills. I think there is a good chance that it is between 1900 and 1918, looking to these bills. However it is just one case and I assume that is just changed gradually. Of course, when one starts using the comma is thousands separator, one uses the dot as decimal mark, otherwise it would become highly confusing.

Here is one from 1878 with a dot: enter image description here

Here is one from 1900 with a dot: enter image description here

Here is one from 1918 with a comma: enter image description here

wythagoras
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    I believe the question is about the decimal mark, not the thousands separator. How are these graphics relevant to the decimal mark? – Rory Daulton Jun 28 '15 at 16:56
  • @RoryDaulton I added this to my answer: Of course, when one starts using the comma is thousands separator, one uses the dot as decimal mark, otherwise it would become highly confusing. – wythagoras Jun 28 '15 at 18:48
  • Thanks for the clarification: I thought that was what you meant, but such things should be made explicitly. – Rory Daulton Jun 28 '15 at 19:18