From: Guy Steele (Guy.Steele@sun.com)
Date: Wed Sep 20 2006 - 11:06:03 CDT
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
U+2006 SIX-PER-EM SPACE
U+2008 PUNCTUATION SPACE
(because then the gap would be equal to the gap caused
by the decimal point?)
U+2009 THIN SPACE
U+200A HAIR SPACE
U+202F NARROW NON-BREAKING SPACE
(because non-breaking is desirable in running text)
What is current practice? What is recommended by Unicode savants?
--Thanks,
Guy Steele
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Appendix
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
groups
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 http://physics.nist.gov/cuu/pdf/sp811.pdf .
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.
http://standards.ieee.org/guides/style/2005Style.pdf
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