solve for a variable

[snowolf]

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

 

[VBcoder]

Go under tools and use the goal seek function. See examples.

 

[snowolf]

Go under tools and use the goal seek function. See examples.

reply
The problem is that dia is never figured out by the formula , and I want to
figure for rpm or sfm at any given time.
example

if the two knowns are:
dia = 0.5000
sfm =800
rpm = ?

or if the two knowns are:
dia = 0.5000
sfm =?
rpm = 6111

So far what you suggested (if I did it correct) can be done with two
different formulas