# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Calibrating a Bris sextant
From: Greg Rudzinski
Date: 2017 Aug 13, 21:48 -0700

Marty,

6th Sun upper limb Hc 45° 56.5'  S.D. 15.8' ref. 0.9'  Hs 46° 13.2'

6th Sun center        Hc 46° 9.8'  ref. 0.9'                     Hs 46° 10.7'

Average fixed angle for 6th Sun is 46° 12'

9th Sun upper limb Hc 55° 58.2'  S.D. 15.8' ref. 0.6'  Hs 56° 14.6'

9th Sun center        Hc 56° 20.5'  ref. 0.5'                   Hs 56°21.0'

Average fixed angle for 9th Sun is 56° 18'

note- The calibrated fixed angle for each Sun is used as the Hs for lower limb, upper limb, and center observations. Try to use the same part of the Bris on all observations.

I hope that you plan to use a sextant (metal) as a standard and alternate observations with sextant and Bris at the beach for a better calibration.

Greg Rudzinski

From: Marty Lyons
Date: 2017 Aug 13, 19:40 -0700

Right now I am just trying to get the calculations under my belt as I am in Princeton, NJ, 25 miles from the coast and a real horizon . So I use a hand level to sight a ficticious horizon and bring the sun in the Bris down or up to it. Not very accurate but it's helps me get working on the principles which I can refine later at the coast.  I have been using the USNO calculators.

Here are a few data points if you don't mind coming up some angles for me.

6th "sun"  , 11 Aug 2017,  Upper Limb, UTC 19:49:57   DR for all N 40 22.545', W 74 40.095'

6th "sun"  , 11 Aug 2017,  Center, UTC 19:48:41         my derived angle 46 10.0'

9th "sun" , 13 Aug 2017,  Upper Limb,  UTC 15:19:09

9th"sun",   13 Aug 2017, Center, UTC 15:21:44            my derived angle 55 53.8'

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