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Lauren Fischer and Paul Frank
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, a space character that is usually 1⁄5 or 1⁄6 the width of an em dash; to insert a thin space using Unicode in Microsoft Word, type the code 2009 where the thin space should appear, set the cursor after “9,” and press Alt + X on the keyboard) 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 (...