NavList:

Randall

Thanks for that. So it appears that a direct approach was used. That is, some other reference was used to bring your surface to 'level' and then the new levels being created are referenced to the surface.

From your talk of finding a level line, instead of a level surface, Intake it that you hunted around on the surface until you found that line.

The 180 end for end flip would then show the same centered bubble, when placed on that line. Got it, I think!

With the vials showing graduations at 10 arc seconds, it is likely that you can estimate to within a half graduation. Thus the mirror on your AH can be set to within 5 arc seconds of level. Because angle of incidence equals angle of reflection we double that, but the overall measured angle through the AH is divided by two, so in my calculation, your systemic remaining error could be 7.5 seconds (just over 0.1 minutes). I stand ready to be corrected on this data point!!

To measure that last bit of systemic error may be possible. Assume you measure 4 altitudes (multi-shot), approximately 90 degrees apart. You may see the eastern altitudes high, while the western altitudes low. Similarly, the northern altitudes low whilst the southern altitudes high. Or some combination thereof. These readings would show the systemic error. Of course, 0.1 minutes of error may be tolerable for your purposes.

Brad

PS I do hope that you haven't fallen into the Bill Morris (New Zealand) versus Brad Morris (New York) trap. With the size of our community, you wouldn't think that our names would be so close. Its just an unfortunate outcome. You wouldn't be the first nor will you be the last to be caught by this.

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