In article , says...

moyo writes:
I'm not real swift with mathematics and naturally suck at Algebra so,
how does a person using his fingers (toes optional) figure the outside
and inside widths of the various segments?

By letting someone else do it ;-)

http://www.delorie.com/wood/segturn.html

Another way -- used by a well recognized segmented turner who just
happens to be an engineer --

He draws the thing full size and then measures off the drawing. He is
good with math but thinks the drawing has lots of advantages.

Bill