Pure math people probably don’t reach for calculators. But engineers do all the time. Back of the envelope guesstimating is bread and butter.

The modern equivalent of a calculator is Excel.

> Back of the envelope guesstimating is bread and butter.

And that is not done with calculators, that is done quickly in your head by having practiced a lot of calculations manually. This is why engineer students still practice manual calculation in college in most places.