Not sure if it's just me but I find it hard to visualize the difference 
between various radii on plane iron edges. I know that if I'm grinding a 
new radius on an iron which has a straight edge, I might draw an arc 
with a compass, then hold my iron against the arc to see how much 
projection or camber I want when grinding. But from then on, it's all 
about camber for me - i.e., how much does the center of the edge project 
beyond the corners of the iron? 1/16th, 1/8th etc. Bigger on a block 
plane or scrub, smaller on a bench plane. Easier to visualize and check 
IME. Exact measurement not so critical.

FWIW
Don

   . aOn 2021-05-06 8:49 p.m., Chris Wolf wrote: