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Sean,

Remember that the correction order is very important when using an artificial horizon. 

1. correct AHs for index error to get AHa

2. divide AHa by 2 to get Ha

3. correct Ha for refraction to get Ho (also semi-diameter if limb to limb)

4. compare Ho to Hc for the intercept

note-there is no dip correction when using an artificial horizon

Greg Rudzinski

From: Sean C
Date: 2015 Oct 8, 21:00 -0700

I recently received a zero magnification sight tube for my Astra IIIb. I tried it for the first time today. I was taking sun sights with my Davis artificial horizon. I must say, I found the sight tube much more difficult to use than the standard 3.5X scope. I got widely varying results when trying to determine index error. (I used the limb-to-limb mehtod.) Errors for the actual sights ranged from +3.4' to +5.3' and my average error for a round of nine sights was +4.7'. I'm going to try some more sights and hope my accuracy improves as I get used to it.

I'd be interested to hear others' experience with it and how you compare/contrast it with a 3.5X or even 7X scope (which I am considering purchasing, as well). Thanks!

Sincerely,

Sean C.