A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Sean C
Date: 2020 Oct 31, 04:07 -0700
I bought another slide rule recently. A Pickett 1011-ES with a heavy-duty case, both in near perfect condition. I was just trying some DR calculations on it and I noticed two gauge marks that I don't understand. On the "ST" scale, there is an arcsecond gauge mark at about 1.18 and an arcminute gauge mark at about 1.97 (both are visible in the picture linked above). After some searching, I found this description of the marks:
"If the mark ' is = 1.970, it is = 206,265 * (180/p) / 60 = 1.97 * 10 5 ; Where, 206,265 = (180 x 60 x 60) / p
If the mark “ is = 1.182, it is = 206,265 * (180/p) = 1.182 * 10 7 ; Where, 206,265 = (180 x 60 x 60) / p"
So, if I'm understanding this correctly, one is the number of arcseconds in a radian multiplied by the number of degrees in a radian and the other is multiplied by 1/60 of the degrees per radian. What would one do with these numbers?
On a somewhat related note: I also found a Japanese company that is still making circular slide rules (including flight computers). Unfortunately, I cannot currently find a way to have one shipped internationally. I am going to try contacting them to see if I can arrange something. So, while I'm at the store ... anybody want anything? Perhaps a bulk order would be more desirable.