A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tony Oz
Date: 2019 Jun 8, 02:34 -0700
I'd rather measured Sun's SD across its' horizontal direction - to eliminate the refractions effects the best possible way.
As Brad has already suggested - I always turn the drum in the "increase" direction (to eliminate the backslash).
And my favourite formula for I.E. determination is:
360° - (360°xx' + 359°yy') / 2
where the xx is the minutes value read directly off the drum for the "on-scale" index position; the yy is the "off-scale" minutes value. This works if the initial I.E. is less than 1°.
The resulting value has algebraic sign and should - as such - be always added to the sextant reading.
Did you study the "Фатьянов А.И. Практическое руководство по выверке и определению поправок штурманских приборов на судах (1976)" book as well?
In the similay way I can obtain the SD:
(360°xx' - 359°yy') / 4