LMS Perfect World

how does attack frequency attack works?
given 2 items with 1st has 0.81af(attack frequency) and 2nd has 1.21af
which is faster?
does 0.81 means 0.81 attack per second or 1 attack per 0.81 second?

The higher, the better. 1.2 is better than 0.78.
3.33 is better than 1.2. :]