With sufficient accuracy, knowing its maximum value, it is possible to
estimate the value of an air-spaced variable capacitor setting just by
looking at it.

Similarly, the value of a coil can be calculated by counting the
number of turns and guessing its length and diameter. The calculation
is simple enough.

I've done it dozens of times. It gets you into the right ballpark.
Which is quite accurate enough for amateur radio purposes. There's no
need for rocket science.

I can't understand the abysmal state of education in simple arithmetic
in our primary schools. We should import the kids who inhabit the
sewers of Rio de Janerio and other American cities and employ them as
arithmetic teachers. It would be more economic than culling by armed
police.
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Reg, G4FGQ