I had a Hp 42S calculator that had a solver program I made for machinists.
There were 3 variables (sfm, rpm, diameter).
If you supplied 2 and punched the soft key of the third it would solve it.
It went like this sfm, rpm, and diameter would be "mvar"
It would recall them in the formula and solve.
The formula would be rpm=((sfm x 12) / (diameter x Pi))

My experience level is with spreadsheets with means, averages,sums, time
calculations.
Just now learning pivot tables