NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The backstaff. was: Re: The Shovell disaster
From: Michael Daly
Date: 2007 Nov 06, 11:31 -0500
From: Michael Daly
Date: 2007 Nov 06, 11:31 -0500
Nicol�s de Hilster wrote: > Given the capabilities of the instrument makers of those days this error > was way beyond their achievable accuracy. Ever since I made my first > Davis Quadrant I checked every example I could lay my hands on (musea, > internet, books etc) and whenever the scale is visible in detail you > will clearly see errors that are larger than that (in general more than > 0.1mm, so just under 1 arc minute). So I take it that on Davis Quadrants > all transversals were linear in those days, unless the cutting plate > wasn't straight. I guess the AutoCAD construction shows that for those instrument sizes, the difference between linear and circular transversals is irrelevant. Thanks for this, Nicol�s. Mike --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---
