A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Ed Popko
Date: 2018 Oct 14, 05:31 -0700
The Lindbergh-Weem's second-setting navigation watch is quite handy in converting Greenwich Mean Time and Equation of Time to Greenwich Hour Angle. However, there are very few guides as to how to actually use this watch. Here are some examples to help out.
In an earlier post about this watch, I showed preliminary PostScript simulations of various watch-face settings. GMT test cases revealed that practical use of this watch is more subtle than first thought due to the interaction of Equation of Time and GMT times less than one minute or for times where the minute hand’s position is counter clockwise relative to the bezel’s 15 degree mark.
Attached is a set of examples that show the watch’s standard 12-hour watch face, AM and PM cases, and a variety of positive and negative Equation-of-Times. One example shows a center-dial rotation for synchronizing the second hand to some zero-time reference such as radio time ticks.
For each watch-face example, I listed the component angles read each of the watch face dials that sum up total Greenwich Hour Angle. I hope these examples help anyone trying to understand this watch. I would appreciate anyone finding errors to let me know.
It is ironic that Longines Heritage Collection User's Flier for this $4,700 watch is completely misleading (see page 16). If anyone understands what they are trying to say, please let me know. Perhaps anyone who can afford this watch is more concerned with dress appearance and then understanding how to actually use it.
Thanks to Gary LaPook for his original NavList post "LHA listing by the minute" (fer3.com/arc/m2.aspx/LHA-listing-minute-looking-for-LaPook-jan-2015-g29895) and to Paul Dolkas for posting "The Ultimate Navigation Watch?" (fer3.com/arc/m2.aspx/ultimate-navigation-watch-Dolkas-aug-2013-g24847). Both got me interested in this watch.