A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2020 Apr 8, 13:39 -0700
Ed J you wrote:
I am looking for instructions for this device and would be grateful if anyone can post a copy or knows how to use this.
Unfortunately, the photo, which is the only one a search google could bring up, isn’t very clear. However, it looks like it consists of three concentric discs, each divided into 360 equal divisions. As the divisions are equal, it can be no more than a simple division and subtraction device for people with no confidence in their own mathematical ability when working under pressure. You could probably write your own instructions. The original instructions probably contained little more than formulae for working out LHA or SHA from GHA, GHA Aries, and longitude. E.g. LHA Star = GHA Aries + SHA Star -longitude W. Of course, we haven’t seen the back; that might be really clever. If the back is clear white ABS plastic, you could write down which formula you needed to remember in soft pencil or spirit-based pen. Spirit based pen comes off with aftershave if you don’t leave it on too long. DaveP