A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2019 Jun 29, 16:29 -0700
That is known as the "0° to 180° meridian arrow"
You will note that it also has a thin line through it which starts from the pole at the center and runs to the edge. With any transparent overlay in place, you will note that the fat arrow and the corresponding thin line are perfectly aligned with your meridian.
This is used to set LHA Aries.
Yes, I clearly understand that the "0° to 180° meridian arrow" is used to set LHAAries - both from the excellent Ed's write-up and from the inadequate original manual. But to work properly I must use the "thin line arrow" to set LHAAries - not the "fat" one! If I set LHAAries with the ""fat" arrow - the overlay points to the opposite part of the sky.
Looks like the team that designed the bases with the U-shaped coursor fell out of communication with the team that created the overlays: the slot on the overlays is turned 180° out of proper position.
Otherwise I like and fully appreciate the idea of separating the adjustments for GHAAries and for DR Lon. Sure less chance for an error.