rule of thumb

It is servility to rule-of-thumb criteria, and a dullness of perception, a timidity in acceptance.

Accurate knowledge is a good thing, but rule-of-thumb experience is often thought to be better.

With such a rule-of-thumb reckoning, you are likely to remain as much in the dark as before.

The knowledge of human nature thus evoked is in no sense science, it is a mere rule-of-thumb affair, a thin mechanical empiricism.

So he's a pretty good rule-of-thumb astrogator, too, and we're computing every element of the flight.