NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Todd Spath
Date: 2024 Mar 8, 08:25 -0800
Art wrote,
"... I have a similar problem with one of my Kollsman periscopic bubblw sextant. For quite a while (about two years after I purchased it) it was giving a fairly consistent required IC. This was across all manner of temperature and humidity and hundreds of individual sights. Then, one day, it started to give ICs that were different for rising objects and falling objects but were fairly constant. Until a little while ago it started to give variable IC. As with your A-12, the IC was fairly consistent for the sight series but would change day to day over about 5' range. Like you, I use a tripod but I am always outdoors..."
Art, have you examined the consistency of your Kollsman averager unit? You mention always letting it run "the full two minutes", but does it run consistently for 120 seconds, or vary somewhat (perhaps with temperature)? Besides checking elapsed time, you can also introduce a step change in the altitude setting at a known time part way through the averaging period and verify that the time weighted average value is "computed" correctly. Check for increasing and decreasing altitude steps and times other than just half of the maximum sample period. I assume you are noting the "half elapsed time" on the rotating dial and subtracting that from your "end of observation" time to get the time to use in the sight reduction, And you are rotating the elevation knob to re-align the (2) index marks before reading the avarage value from the drum? If you rewind the averager (lever reached with right hand) before you get the proper average (per above), the index marks get reset and the drum would show the final elevation instead of the average. Forgive me if you are aware of all this.
