NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Beginner / Davis Plastic Sextants
From: Frank Reed CT
Date: 2005 Oct 6, 18:50 EDT
From: Frank Reed CT
Date: 2005 Oct 6, 18:50 EDT
Bill you wrote: " The *really* nice three-arm-protractors like Alex's Soviet unit can be dialed in to 0.1' if I recall, so would demand input of equal precision and accuracy for optimal results. " An angle of 1 minute of arc is (and I do mean *IS*) a ratio of 1 to 3438 (10,800/pi to be exact). So an angle of 0.1 minutes of arc is a ratio of 1 to about 34,000. The distance "across" the object(s) and the distance "out" to the object(s) are in a ratio of 1 to 34,000 when the angle is 0.1 minutes of arc. Given that, is there any chance that this tiny angle could be meaningful in plotting with a three-arm protractor?? Assuming that the chart itself is, let's say, one meter across, if I extend a line all the way across the chart and shift the end-point by 1 millimeter, I'm making an angular shift of only 1/1000 or in other words about 3 minutes of arc. No horizontal angle (as between buoys) would ever need to be measured to an accuracy better than this for live navigation. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars