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A set of instructions come with Celestaire's 'Practice Bubble'.  They provide
a correction that you have to make for the particular sextant.  In the end, it
replaces the Dip correction in your calculations.  Without this, your observed
altitude can be really wrong.

Standing on dry land, it works pretty well. If I recall correctly, they
advertise plus or minus 2'.

I believe it.



On Mon, 16 Dec 2002 15:49:13 -0500 Marc Bernstein 
wrote:

> I assume most of us are using the "practice
> bubble horizon" sold by
> Celestaire. The key word here is 'practice'. It
> is not particularly easy to
> sight through and the bubble is quite wobbly.
> The main problem appears to be
> a lack of fluid dampening. Based upon my
> experience 7 minutes is not bad. I
> often get accuracies of 10-15 minutes. Maybe I
> need more practice.
>
> By the way if you hold a flashlight in just the
> right spot, it is possible
> to illuminate the bubble from the outside so
> you can use the practice bubble
> at night also. This only works with the Moon.
> There is not enough light
> transmission to sight a star, and no
> magnification.
>
> But for those of us who are landlocked it is
> still worth it.
>

   

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