Sometimes people want to compare the degree of clustering or spread between two sets of numbers that have completely different units: banana weights and heights of trees, say. A sophisticated (and slightly hypothetical) manager might want to know how the various sizes of all the law firms used by a law department compare in their distribution to the third-year annuity costs it pays for all its patents. How do you compare two unrelated data sets? A statistical measure called the coefficient of variation (CV) does the trick.
The CV is the ratio of the standard deviation to the average of a set of numbers. You divide the standard deviation of a set of numbers (which Excel does instantly) by the average of those numbers (ditto).