I used to use my HP-41 to help confirm my results. I wrote numerical integration, differentiation and other solvers for it. I would enter the equations and pa

I used to use my HP-41 to help confirm my results. I wrote numerical integration, differentiation and other solvers for it. I would enter the equations and parameters and then work on the problem by hand. Once done, I could look at the result on the calculator and confirm the probability of my answer being correct within a reasonable degree of certainty (in most cases). I think I learned more this way than by simply memorizing equations.