I keep a slide rule in my shop room (sometimes a darkroom to develop B&W)
to determine the size of pinholes, using Captain Abney's formula, which
involves the square root of focal length. I seem to have lost the ability
to do square roots manually.
I had a semester-long class on the slide rule in engine school, and the
most important thing I learned was the basis of its construction. While
working as a consulting engineer a few years later, I developed a special
application slide rule to easily determine the answer to a problem of
scheduling that occurred many times a day in a client's business.
Marty
