When I was in

calculus at the

University of Minnesota everyone either had the

HP 48G or the

TI-83 calculator. Now the TI (

Texas Instruments) was far easier to use, it had graphing, and advanced math functions but it also worked just like a normal calculator. The

HP was much more powerful (could solve integrals, graph 3d equations, etc) but used RPN. This made it highly entertaining when someone asked to borrow your calculator during a test and could not for the life of them figure out how the damn things worked.

RPN is sort of like learning to touch type. It takes a while to get used to, but once you are good at it, it makes things a whole lot easier.