Here is something I should be able to figure out but can’t. I have a
Sargon model 652 DRO now on my lathe. (It has no numeric key pad). How
do I zero this thing so I can get a direct radius or diameter reading
for a bar I would be turning?

The radius is off by a factor of 2 and the diameter is off by a factor
of 4.

TIA

Jake in Escondido