NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2013 Dec 28, 23:34 -0500
Hi Alex
I will quote directly from Nicolas due Hilster's page I referenced earlier
Quote
On October 11th, 2005 and November 5th, 2007 field tests were conducted in which the Davis Quadrant was involved. The first test was done with instrument number 3, the second with number 4. Both tests showed that the Davis Quadrant tends to measure too high, unless the upper limb is measured. The first test, where the lower limb was measured showed an average error of +11.5 arc minutes, with a standard deviation of 8.7 arc minutes. The second test showed an average error of +10.5 arc minutes with a standard deviation of 5.1 arc minutes (calculated over the second part of the trial, see graph). The reason for this is the shadow method used, which was first described by Thmoas Hood in 1590 in his The Use of the Jacobs Staffe., and which used only one edge of the shadow of the shadow vane. As this shadow has a 31 arcminute penumbra due to the sun's diameter it is unevitable that error in the observation will occur.
Unquote
[ I do hope that Nicolas will see this post and participate in the discussion.]
I will suggest that Nicolas is not an expert in the use of the Davis Quadrant in any sense of the word. There is no suggestion of thousands of observations or hundreds of hours of experimentation. Presented are two short term trials in which Nicolas obtains altitude results. Results which Frank claims are the best we can expect.
Brad
Frank, > For the potential accuracy of backstaffs and other pre-double-reflecting > instruments, I suggested 10 minutes of arc. I want to clarify that this is > being generous. Under excellent conditions with a fine instrument and > top-notch observer, that's the best that you should expect. A reasonable > expectation for normal conditions and normal observers and instruments > would be 20-30' (in the 1 s.d. sense). How can you justify these statements? Any experiments? References? I do not mean the general common navigation errors, which can be attributed to many reasons. But any direct evidence of a backstaff performance. Alex.
