# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Artificial Horizon Levels
From: Fred Hebard
Date: 2004 Mar 28, 13:41 -0500

```Robert,

It sounds good to me.  You would want a firm, flat surface, clean and
without irregularities, such as new sheet of glass.  It also would be
important to orient the level between readings on the exact same spot
as possible, and you might want to look at the scatter in the readings
from having picked the level up and put it back down without rotating
considerations.

Even buying an ordinary level for carpentry work, it is surprising how
many of them, especially the more inexpensive ones, give a different
reading depending upon the orientation of the level.

Have you tried to calculate how accurate a sextant reading would arise
from having leveled the mirror to 30 seconds of arc?

Thanks,

Fred

On Mar 28, 2004, at 1:30 PM, Robert Eno wrote:

> Hello List,
>
> A question to ponder.
>
> I have a Freiberger flat glass artificial horizon that came with two
> longitudinal levels which are senistive to about 30 seconds of arc.
> They came already calibrated but do have a provision for adjustment.
>
> I've had this item for about 10 years and have never dared tamper with
> the adjustment screws on the levels, however, it would be useful to
> know how to calibrate them. My initial thought is that in order to
> calibrate them, one must have a surface that one knows for a fact, is
> perfectly level, however, this is unrealistic for the average person.
>
> I have stewed over this problem and decided that logically, the way to
> calibrate the levels would be to find a spot that is reasonably level,
> then place the level on that spot and note where the bubble lies
> within the graduated lines on the level. Then one would turn the level
> 180 degrees on it's longitudinal axis and again note the position of
> the bubble. The bubble should be within the same spot; if not, then
> one would have to adjust the screw until the bubble moves halfway to
> its desired position. Then one would again turn the level 180 degrees
> and do it all over again and keep going back and forth until the
> bubble rests in the same spot.
>
>
> Am I on the right track here?  For that matter, am I making any sense?
>
> cheers,
>
> Robert

```
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