A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Mark 15 sextants
From: Greg Rudzinski
Date: 2019 Mar 1, 07:43 -0800
With the Ebbco sextant the index error can change +/- 2' depending on temperature but the average index error seems to hold steady. Another important correction is arc error. The Ebbco I'm working with has arc errors as high as 6'. There are a few ways to determine arc error. Use an artificial horizon and work up the arc error to apply to get a zero intercept using the GPS position as the assumed position. Do this through every 10° of arc and keep the table with the sextant. The plastic sextant arc error cause is from a perminent warping of the sextant arc.
From: Michael Bradley
Date: 2019 Mar 1, 00:58 -0800
Back in Oct 2018 you wrote
'I have restored filters on four different EBBCo's with success using solar film and layered post optomitrist exam sunglasses. It is easy to pop the plastic filter retainer ring out then cut to fit the film using the original filter as a template. Pop the plastic ring back in over the solar film and you are good to go with bright sunlight.'
What repeatabilty did you get out of the restored Ebbcos?
The copy I have shows systematic errors of up to 6', down to prismatic defects in the shades.
IE on a star 0.0' - no shades
Swap around the heavy index shade and the heavy horizon shade on sun sights and the average difference between sights is 6'
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