NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: AN5954 bubble octant by Bausch and Lomb
From: Alexandre Eremenko
Date: 2012 May 4, 18:39 -0400
From: Alexandre Eremenko
Date: 2012 May 4, 18:39 -0400
Gary, No, unfortunately this is a different (earlier) sextant by Bausch and Lomb, which uses an averager. In general, the marking of these US Navy octants is extremally confusing. For example AN5851-1 is also Mark V, but is has the varieties 3014-1-A, 3014-1B, 3014-1-C, 3014-2-A, 3014-2-B, 3014-2-C, 3014-1-D and 3018-1-A, and all these are different:-) Is this to confuse the enemy intelligence? :-) Alex. On Fri, 4 May 2012, Gary LaPook wrote: > > See if this helps. > > http://fer3.com/arc/imgx/A-6-Octant-Manual.pdf > > "Don't let the perfect be the enemy of the good." > > For use in flight, the median is "good enough" (especially considering the magnitude of the other possible inaccuracies) and a whole lot easier to derive than the average for a changing altitude. Many octants used this method, A-7, A-10, A-12 and your B&L and probably others. > > gl > > --- On Fri, 5/4/12, Alexandre E Eremenkowrote: > > From: Alexandre E Eremenko > Subject: [NavList] AN5954 bubble octant by Bausch and Lomb > To: NavList@fer3.com > Date: Friday, May 4, 2012, 1:53 PM > > > Dear List members, > > Does anyone have this octant or a manual to it? > I see a picture and a description in Ifland's book. > Unfortunately this description makes no sense for me:-( > > The main distinction from all other air octants is that > it is "medianizing" instead of averaging. > Instead of averaging it takes a median of 15 altitudes, > with a very simple "medianiser". There is a picture which > is supposed to show this medianiser in action, and it seems > clear how it works. > > Let me recall what is the median. You order 15 numbers by their > magnitude and take the 7-th. This is the median. > Median has some substantial advantages in comparison with > the average, if you repeatedly measure the SAME quantity. > > This does not apply however to sextant altitude observatons, > except for the Polaris and Sun at Noon. > In general, altitude changes quite quickly and when you take 15 shots, > the results are very likely to be increasing or desreasing. > In which case there is evidently no point of taking the median. > (It will be simply the 7-th shot). > > That's why I am looking for a more reasonable explanation of how this > sextant really works, or what is it for. > > Alex. > > > > > > > > > : http://fer3.com/arc/m2.aspx?i=119377 > > >