Question about formatting numerals

From: Guy Steele (
Date: Wed Sep 20 2006 - 11:06:03 CDT

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    When numerals are to be formatted in formal scientific texts
    according to the custom of using space to separate the digits
    in to groups of three, as in "27 312 416.315 67 m/s",
    what is the recommended Unicode character to use for
    this separation? Obvious candidates are


         (because then the gap would be equal to the gap caused
         by the decimal point?)

    U+2009 THIN SPACE


         (because non-breaking is desirable in running text)

    What is current practice? What is recommended by Unicode savants?

       Guy Steele


    I have checked with NIST and IEEE. NIST Special Publication 811 (1995)
    at recommends use of "a thin, fixed space":

       10.5.3 Grouping digits
       Because the comma is widely used as the decimal marker outside
       the United States, it should not be used to separate digits into
       of three. Instead, digits should be separated into groups of three,
       counting from the decimal marker towards the left and right, by the
       use of a thin, fixed space. However, this practice is not usually
       followed for numbers having only four digits on either side of the
       decimal marker except when uniformity in a table is desired.

    See .

    The style file for IEEE standards specifies grouping-by-threes only
    for tables,
    and specifies only the use of "a space":

       15.4.2 Numerical values
       To facilitate the comprehension of numbers, digits should be
       separated into groups of three, counting from the decimal point
       toward the left and right. The groups should be separated by a space,
       rather than by a comma, period, or dash. If the magnitude of the
       number is less than one, the decimal point should be preceded by a
       zero. In numbers of four digits, the space is not necessary, unless
       four-digit numbers are grouped in a column with numbers of five
       digits or more.

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