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Re: bubble sextant index error
From: Frank Reed CT
Date: 2005 Dec 14, 14:41 EST
From: Frank Reed CT
Date: 2005 Dec 14, 14:41 EST
Paul Hirose, you wrote: "I have seen collimators of that type at a survey equipment shop. Three were attached to a heavy vertical I-beam to provide artificial targets at approximately +45, 0, and -45 elevation. Their optical axes intersected just above a pillar a few feet away, on which the theodolite under test was mounted. Maybe a marine sextant could be tested with that setup. You'd have to hunt around for the sweet spot where the collimator beams hit the index mirror and horizon glass simultaneously." Yes, that's a setup I've seen described. You can mount as many of these as you want on a large table. Where the beams cross, you have the equivalent of infinitely distant sources at fixed angular intervals. Measure those with any good instrument, a reliable sextant or a theodolite, and then any other instrument placed there can be tested to high accuracy. This is one good way for measuring arc error. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars