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I read that different cultures have different ways of grouping digits before the decimal point for readability e.g. 1234567890 can be grouped as 1 234 567 890 (English), 12 3456 7890 (Chinese) or 1 23 45 67 890 (Indian), but is there an established convention for grouping digits of a real number after the decimal point for readability e.g. should 3.14159265358979 be grouped as 3.141 592 653 589 79, 3.14159 26535 8979 or something else?

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Interesting. I've never thought to worry about this. Using the spacing appropriate to the left-of-decimal digits, having fixed a language, seems appropriate, except that now it's the last group that may be too short, instead of the first (in the English and Chinese conventions.) – Kevin Carlson Aug 15 '12 at 11:25
I can't say much of this due to my brilliant ignorance in the issue, but I think the main motivation for grouping to the right of the decimal point, just as it is to the left, is for clearity, and if this is really so then I guess there can't really be any universal convention about it. – DonAntonio Aug 15 '12 at 12:03
It could be that the decimal point is an anchor from which both integer and fractional parts "grow" out of, leftwards and rightwards, respectively. – Gnubie Aug 15 '12 at 19:11
It also ensures the groups are aligned when using decimal tabs, i.e. aligning a column of numbers at the decimal point, e.g. to add them up: – Gnubie Aug 15 '12 at 19:12
up vote 3 down vote accepted

The only convention I have come across is that many publications of mathematical vales tend to group the digits after the decimal point in blocks of 5, so that Pi would appear as 3.14159 26535 89793 ...

You can see examples such as this on Wikipedia, but I have never heard of any official or widespread convention about this.

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One thing I found is the Swift programming example about decimals Numeric Literals

let oneMillion = 1_000_000
let justOverOneMillion = 1_000_000.000_000_1
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