2.1.1329 Part 1 Section 20.1.10.40, ST_Percentage (Percentage)

a.   The standard states that ST_Percentage is read and written as a percent with a trailing percent sign.

Office will read percentages formatted with a trailing percent sign or formatted as 1000th of a percent without a trailing percent sign, but only write percentages as 1000th's of a percent without a trailing percent sign.