The concept that I learned in past 2 days is this: Days Sales Outstanding (DSO) and the way you calculate it.
Joshua Burnett has posted an article on this way back in March 2009. Read it here: The DSO Calculation (Days Sales Outstanding).
It’s quite simple and yet very deep in concept. I simply loved to read and learn. I am sure it would be useful to some people out there, trying to understand what DSO is all about.