I have a small HF lathe that my kid & I putz on, no high precission
work etc.

I'm keen to learn any tricks from the old masters regarding turning a
piece down to a specific diameter. For example, say you need to turn
a 10 mm rod down to 8.5 mm, are there any fancy compound slide angles
that equate closely to the dial, or do you guys just "shave and
measure"?
Bear in mind this is rudementry bushings & such, but I would like
to learn a better way.

Any tips much appreciated.
Thanks.