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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Chuck Varney
Date: 2023 Jun 27, 18:19 -0700
Marty Lyons and Frank Reed,
A few years ago I saved two Abney level documents: Abney Levels – Uses and Applications with Appropriate Tables (Keuffel & Esser, 1950) and The Abney Level Handbook (U.S. Forest Service, 1927).
Both documents provide a method to correct a condition where the line of sight is horizontal and the index is set to zero, but the spirit level bubble is not centered. I have attached the pertinent pages from each of them; the K&E pages first (3. Bubble section), followed by the more detailed Forest Service pages (Glass Vial Parallel to Line of Sight section).
In both cases they establish a horizontal line of sight between two points (separated by 30-50 feet in the K&E case and 100-200 feet in the Forest Service case), sight one end of the line from the other with the index set to zero, then if the bubble isn’t centered, adjust the spirit level to center the bubble.
Chuck V
_p6-8.jpg "Click to enlarge.")
