NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Randall Morrow
Date: 2013 May 10, 12:38 -0700
Norm,
You are coprrect. The AH mirror shown is a second surface mirror. I had previously installed a first surface, which I liked better and at low angles, it probably gave more accuracy. It certainly decreases "visual ambiguity" as to the exact center or exact tangency of a sight. But the errors are likely within the margins of error for all the other factors involved in sight taking so it is not important to me. I will trade up to a fisrt surface as soon as I can, but mainly to make what I see more pleasant to see, (no blurring) than to get accuracy improvements. I was not aware of the issue of "wedge angle" and assumed the second surface abberations were due to there being 2 reflections that separate from each other as the angle of view decreases.
The 10 second vials are over-kill of course, again because of the many other sources of error. In an earlier post I mentioned a hardware store torpedo level that was aouund 10 minutes accuracy and costs $10.00. But I enjoyed the project and mine look way cooler! It is something of an attempt to create the antique AH with 2 spirit levels such as the Elliot. (picture attached) Something like this was used on many explorations such as Amundson at the south pole. Thank you for sharing your comments. Regards, Randy
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