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    Re: Star to Star Distances taken on a Second Hand Sextant
    From: Michael Bradley
    Date: 2019 Dec 8, 14:00 -0800

    A quick response to some of the posts in this thread, just back from a short trip.

    The Context. This whole thing is part of a project using personal time rather than money to identify a navigationally useful minimum system, including choice of sextant. Doing for 50 monies what any **** fool can do for 500 or 1500. I have a target error budget of 1' each for sextant limitation, which for a cheap sextant will be 4 hits of 1' each, arc errors, shade errors, and constancy ( with respect to the passage of time time ) and stability ( with respect to  environmental variables such as temperature). Having renewed the shade glazing on an Ebbco, I'm down to arc errors, and if that measurement also throws up the  temperature sensetivity of Index error, and a useable value of settling time of Index Error after a temperature change, all to the good. 

        

    David - the 'swing through' technique you worked up is identical to the technique I came to.

    Fred - Star on itself Index Error checking is meat and drink to me, has been my favourite for years, it's especially suitable after an evening of maintaining/tweaking a sextant.

    Brad - two distances recorded on the same date comment - try the EP and Observation Date and Time in a sight planning application - you will see how conveniently the Plough/Dipper handle (Alioth, Alkaid, and Dubhe) and Arcturus are set in the sky. That  was the most productive night - managed two distances that night.

    Brad - data sets - as the text of my initial post states, I took sets of 5, with 5 Index Error measurements in between, after the sextant had settled ex backpack, reporting means only. I didn't keep the ensemble data. I'm perfectly content to 'publish' as is - the technique is refutable (or not) by the standard scientific method of having a go at it yourself. We all have access to the same night sky.

    Thanks for your interest

    Good Navigating

    Michael Bradley

       
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