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Bruce, you wrote:
"Now there is an Iphone app that uses the camera to measure angles. Match that 
with celestial navigation apps and we would have our digital pocket sextant."

But it's still an iKamal. And what I mean by that is that it is limited to the 
angular accuracy that can be obtained with any simple "angle-filling" device 
that is held in the hand. Expect no better than half a degree of acccuracy 
EVEN IF the internal vertical is absolutely accurate (and it's not).

However, I do know a way of using -two- iPhones to make a good sextant. You 
see, the face of the iPhone is quite reflective :-). So we take two iPhones, 
power them down, affix them perpendicular to a backplate, one on a rotating 
arm, and then when held so that sunlight or starlight bounces from one iPhone 
to the next, the angle between a direct ray from the horizon and the 
reflected ray from the two iPhones will not change when it is rotated about 
an axis perpendicular to the backplate. Ha! Yes, it's just a sextant with the 
two iPhones being used as horizon and index mirrors. Until the phone can 
capture the video and analyze the image (presently it cannot except by 
hacking), the iKamal cannot beat the accuracy that comes from 
double-reflection. 

And also, needless to say but I will say it anyway, the accelerometers for 
determining the vertical in these new phones (many models now have them --not 
just the iPhone) are sensitive to observer accelerations unless some rather 
sophisticated processing is performed to average those out.

-FER



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