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Frank

You wrote, in commenting on R B Gordon's paper in the Journal of the Royal 
Institute of Navigation (1964) 17. pp 125 - 147:

"The author describes 
his attempts to measure INDEX ERROR using stars. He describes his miserable 
results which he clearly cannot explain, and then from that experience he 
asserts (without evidence; without data; much as you have done) that 
star-star sights for arc error wouldn't work. He has ZERO data on the topic 
of using star-star distances for arc error."

What you say about his lack of data is fair enough, but isn't estimating index 
error by using a star the simplest case of a star-star sight? If one accepts 
this, may we then accept that sights using two stars are likely to have 
similar errors? In my case, using a SNO-T sextant with x6 telescope clamped 
atop a theodolite tripod the standard deviation of index error observations 
using a star was 0.17 minutes (n = 30). 

I am not a fan of Galilean 'scopes and Gordon seems to have been particularly 
unlucky with his if he found "...a star image will superimpose  over a range 
of 5'."

Bill Morris
Pukenui
New Zealand


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