NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bygrave slide rule
From: John Rae
Date: 2005 Dec 11, 18:53 -0800
From: John Rae
Date: 2005 Dec 11, 18:53 -0800
I, too am interested in studying the operation of a
Bygrave Slide Rule, so any information about them would be welcome.
Making a sample would be a good winter
project. Last year I made two circular slide rules using plastic discs and
gluing up computer generated scales, obtained by downloading from www.sphere.bc.ca/test/build.html
. The longer scales of these slide rules are useful, but I still feel more
at home with my trusty mahogany Log-Log Duplex Trig. (or an HP
calculator!)
It seems to me that a good slide rule would be good
for use with bubble sextants, where 1 minute is about the very best one can
expect.
I have two different bubble sextants, Mk V (US) and
Mk IXa. With my unsteady hands and eyes when I take observations from
a fixed location, in groups of 5, without the averaging device, and plot the
results and/or take the median value of the reduced sight, I get spreads of
about 10 to 15 minutes on an average (good?) day, but usually the median value
is much closer.
I recently talked with a good friend of mine who
was an airforce navigator ca 1950, who still has his log book. He claimed
to have records of several thousand sights using a Mk IXa, mostly on long
range flights north of 65. He got better results than I do, but was
elated when accurate electronic navigation became available ca
1952.
