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Marcel,

If you look at my original results:

Alioth Alkaid Hc 31*37*
10* 27.1' observed distance by sextant
+0.3' refraction correction by table
10* 27.4' true distance
10* 27.6' true calculated distance by William's on-line calculator
Low 0.2'

You will see that the true distance William's calculation using USNO data is 10* 27.6' vs. Paul's true distance calculation 10* 27.66' for a difference of .06'. Not much of a difference. What you see listed as true distance in my original post is the sextant distance reading corrected to true by adding a refraction correction of 0.3'. The difference between my corrected to true sextant observation and the calculated true distance is 0.2' so my sextant was reading low 0.2'. This means that an index correction of 0.2' needs to be added to the sextant reading. It looks like everyone has close to the same numbers.

Greg Rudzinski
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