A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Francis Upchurch
Date: 2016 Sep 2, 01:09 -0700
I think Frank has already answered your questions better than I could have done.
My new enlarged version of the Nocturnal is on the boat but I'll get some photos and send next week.
I have so far only used it for 2 main purposes.
1) Polaris altitude correction . You are basically lining up polaris through the center and estimate LHA of Cassiopeia trailing star. This is lined up with the "Y" axis graduated in + or Minui 40'. So the angle of LHAmeasured to the nearest degree or so ( a bit better with Vernia) immediatedly gives the poalris correction to the nearest minute!
2) can be used to estimate longitude by measuring LHA kochab as per Tony Crowley book.