A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2019 Apr 5, 01:50 -0700
Jacob M. Huffman you wrote:
The proportional divides were one of the most useful nav tools I ever had. Setup is simple: slide the set screw with pointer to your groundspeed and tighten the screw. Open the wide end to the exact distance between two points, then carefully set the narrow end against any convenient scale or line of longitude. The distance between the points is the estimated time enroute (ete).
Well I’ve never heard of that before. Mine only have draughtsman’s scales for lines on one side and for areas on the other, and they’re the best the Government could buy. They’re normally only used at the planning and analysis stages when working between drawings, maps, charts, photographs, and radar photographs of different scales. However, it turns out the Weems and Plath ones are also calibrated for S=VT
Take care using them as normal dividers in the confined space of a yacht or aircraft cockpit. If you go over a bump, there’s a danger of the necessarily sharp points at the top end piecing your life jacket or worse. DaveP