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Bill,

3' average intercepts using an artificial horizon is high even for a plastic sextant. If using a metal sextant then the worst intercept should be no worse than 1'. 

Things to check:

1. Water tray protected from wind.

2. Scope focused with body centered in field.

3. Filtered Suns should be equally dim.

4. Compare upper, lower, and overlapped observations to see which works best for you.

If you are using a plastic sextant then hold lightly. Check index error before and after each observation. Worst result should be better than 2.5' with plastic.

note - There is no height of eye correction.  Index error is applied first to the artificial horizon measurement before halving. The refraction correction is derived from the halved artificial horizon measurement.

Greg Rudzinski

From: Bill Lionheart
Date: 2016 Feb 24, 03:37 -0800

My sun sights using a tray of water for an artificial horizon in my garden seem to be too low by about 3 minutes. I have corrected my sextant for index error. I's there anything else I should look out for? Could it just be poor technique? Could I have errors of this size in my arc? If I can't do it in ideal conditions in my garden I will be worse at sea!