A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2019 Jun 8, 04:28 -0700
You have o.2' of index error on the arc if + is on the arc and minus off the arc. Be careful when reading the micrometer drum minutes off the arc. Right now the semi diameter is about 15.8' so a full diameter will be 31.6'. Your reading on the micrometer drum should be close to 31.6' on the arc and then 28.4' off the arc (60' - 31.6') for zero index error. Not a good idea to just use the on the arc measurement.