Thank you for all the replies! Now I understand RPN is born for engineers XD

But school work is somewhat different. Here is my example.

To calculate the motion radius of a charge :

r=m*v/(q*B)

So I write the formula on my test paper first, then get my calculator, find out the value of variables from the question, and input them. Using natural display, all the values in the expression are just in there correct positions, corresponding to the formula.

*Edited: 5 May 2013, 4:34 a.m. after one or more responses were posted*