The sextant images (Davis Mark 3 with sight tube ?) seems to be showing around 5' of index error off the arc. Were you able to zero that out ?
I have been eavesdropping on this forum for several months now - probably understanding less than 1% of what is discussed, but nonetheless inspired by your passion and vast knowledge.
I come to the subject from a very different angle - that of an artist. I did grow up sailing around Vancouver Island (I currently live in Halifax), and my father is a master mariner who has, with mixed results, tried to teach his daughter the basics of sextant use and navigation (though I'm realizing that books, and someone not related to me, may make this process less frustrating!).
My work is an ongoing documentation and exploration of the subject of navigation (and the weather), though often in the abstract. I'm slightly obsessed with Bernard Moitessier and his way of making the practical aspects of sailing both poetic and philosophical.
In any case, I invite you to view my current exhibition in Toronto entitled 'The captain knew too well where he was' (which many of you may recognize as a Joshua Slocum quote - applicable, I think, to both navigation, and to life...) http://www.juliemgallery.com/#!carly-butler-/c1opt
Thank you for letting me lurk and learn, and please forgive this off-topic posting...
All the best,