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George, for the sake of brevity I omitted the things that I was not seeking 
discussion of. But since you asked...

<1. I am puzzled by what Jared says about checking index error. >
 I did check the index error before taking sights. Perhaps you are familiar 
with the Cassens & Palth design which puts a large index error adjustment 
screw at the end of the vernier? That's what I was using, and in the cold 
with gloves I *suspect* that I loosened the screw and tightened it again as I 
went back and forth, so that I unlocked the wheels and the zero slipped. This 
*after* I had checked that it was zeroed, during the sightings.

I have now tightened that screw strongly enough so that it will not accidentally come undone.


 Why? If it is the same temperature at both times, what should change? And 
given that a high sighting of a pinpoint object is going to be sharper than a 
low sighting of a somewhat large object in disturbed air...Why not?
 Note that I am not relying on the zero from the previous night--I am checking 
it against the horizon on the following day anyway. But I have found that in 
the same temperature, a zero from a pinpoint light source will be easier and 
more accurate than from any other source.
 One of the other things that I didn't mention for brevity is that I have some 
sight damage from LASIK. The pinpoint light source from a star is also easier 
for me to use than a horizon or sun disk.

2.  Nope, didn't say they were. The 
winter means that I will be dealing with a lower sun though. I said late 
winter afternoon, and around here that means the sun is near 28 degrees at 
high noon, 14 degrees at mid afternoon, and somthing like ten degrees or less 
in the late afternoon.

Compare the atmospheric effects for a sighting at ten degrees to a typical 
summer midday sighting at altitudes that neer come near ten degrees. THAT's 
the effect of winter.

<>
 Thank you George! That's the point that I was asking for a response on. 
Although, you still haven't responded on the main point: What kind of 
position accuracy do YOU get with a sextant under similar circumstances? How 
tight a cluster and what absolute position accuracy? Can you get 2/10th's of 
a mile with a rough horizon and an Ho on the order of 10 degrees? 1/2 mile? 1 
mile?

 Yes, and that is accounted for.

   

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