2.1.1042 Part 1 Section 18.17.7.299, STDEV

a.   The standard maps x to the sample mean and n to the sample size.

Office maps x-bar to the sample mean, n to the sample size and x to a sample value.

b.   The standard does not specify what happens if sample size is less than or equal to 1.

Office returns #DIV/0! if sample size is less than or equal to 1.