A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Hanno Ix
Date: 2015 Feb 20, 10:48 -0800
With the goal to create something like the Bygrave or Fuller I created 2 versions of 4-digit circular sliderules. Actually, I did not really succeed - nor need I, I believe, since the hav-Doniol is probably a better way of sight reduction. But once I had started with this project I had so much fun that I proceeded. There are 2 versions, the difference is in the way the proper spirals are found. More later. I show you here only the faces but I will soon report details of finished versions. I am sure there are many of you who can create the necessary pointers and the pivot by themselves. Therefore I am not showing mechanical drawings since the implemantation of those depends strongly on one's skills and tools, although I will asist you with details if such are requested. The only thing is that you have to be rather precise when you build one of them. The materials are easy to come by.
Also I do not describe here - yet - the usage. If you have used a circular sliderule before at all you will find out quickly by yourself. Two hints, though: (i) Both use a 2-step process whereby one first decides beforehand, by means of colors and an auxiliarly sliderule located at the rim, on which spiral one will find the proper number location. (ii) The scale is rather particular in that it uses alternatively black and white flields for the number positions. This way I needed only to draw half the number of marks which made the high resolution possible: black for the even steps, white for the odd. Multiple of five's are additionally marked with a dot. I was surprised myself when I saw how easy it was to identify a particular number once the right spiral was determined.
You may scale the .pdf file drawings as you wish. I have built a 12", a 10" and a 8" diameter version with equal ease. The bigger ones allowed me to print a haversine table on the back, the small one's back is a good place for the azimuth diagram. As I said, though, neither one is a complete solution but both yield excellent results.
Let me leave you with this for today. I am eager to hear from you re: suggestions and criticisms.