NavList:

Thanks for the reply Gary. That’s sort of how I got to this point except by looking at a distant object on land.
But, when I take something apart, I tend to make things messier. I took the counter off too. 😔 So, I’ve got several unknowns.
At this point I’ve started over. I had several things crossed up so I pulled the top prism again. With a magnifying visor plus a swing down loupe, I think the threads are 70 teeth per inch at a radius of 1.630”. For one tooth, that’s (1/70)/1.630 = 0.00876 and tan-1= 0.502 so, Yes it’s 30 minutes per tooth.

I sighted at a piece of 3/4” white plastic pipe at about 140’ and ended up with the views matching at 0 degrees 10 minutes. I’ll just do some shots with a 10 minute correction before I try anything else.
Regards, Noell