18.4.3 Number Spacing
By SI convention, the decimal point is the only punctuation mark permitted in numerals, and it is used to separate the integer and decimal parts of the number. The SI does not use commas in numbers, in particular because the comma is used in some countries as the decimal sign. Integers (whole numbers) with more than 4 digits are separated into groups of 3 (using a thin space) with respect to the decimal point. Four-digit integers are closed up (without a space). Decimal digits also are grouped in sets of 3 digits beginning at the decimal sign, with the same closed-up spacing for 4-digit groups. (See also 19.1.1, Numbers and Percentages, Use of Numerals, Numbers of 4 or More Digits to Either Side of the Decimal Point).
12 345.678 901
1 234 567.8901
However, certain types of numerals that have more than 4 digits are expressed without spacing, such as street addresses, postal codes, page numbers, and numerals combined with letters, including trial registration identifiers.
Chicago, IL 60610
This study was supported by grant MCH-110624.