A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2020 Mar 26, 16:11 -0700
After three days and nights of clear skies, I thought I ought to get a sextant out to practise with before the weather changed, which it’s forecast to do from tomorrow. I decided to see how my 1942 Hughes MKIXBM 4077/42 last professionally maintained and calibrated by Fenns in 1965 coped v Venus using Anti-Spoof Pro as the master. Trying to see anything less bright would have been a waste of time with the light pollution around here. When I went to set the temperature and pressure, it seemed remarkably close to the current true local values. Then I noticed that as the night got colder, the app temperature was reducing automatically too, something I’d never noticed before. Is the app getting temp & press from somewhere? I notice that on the settings page there are tick boxes annotated Net Wx, SL Pressure, and DOV. Do those have anything to do with it? Also, what does each stand for?
Results wise, it was generally overreading by about 5’ of arc, which I suppose isn’t bad for an aircraft sextant that hasn’t seen the inside of a professional maintenance laboratory for 55 years. Oh, and Geoffrey Kolbe, I tested the ‘tilt invariance’ while I was at it. It’s pretty good, except there’s a slight delay, ‘stiction’ or the fluid equivalent, not quite Coulomb hang off error, because wiping across the chamber from near bottom to near top, the bubble always gets there in the end and coincides with the star about a second after the sextant stops moving. DaveP