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mjans,

How about telling us exactly what model sextant you have?  It makes a
difference when positioning the body with respect to the bubble.

Ken Gebhart
On Aug 27, 2010, at 4:41 PM, mjans wrote:

> Hello,
>
> I have recently acquired my grandfathers WWII Bubble sextant. He
> has long passed away and left me no instruction on how to use it.
> No manuals, no spoken wisdom, nada... I've figured out how to make
> the bubble and how to collapse it, etc.. but still haven't quite
> figured out what corrections I need to apply to the sighting. When
> figuring out Ha from Hs, would I need to apply an Index correction?
> Since there doesn't seem to be an index mirror, I don't really see
> why?
>
> When taking a sighting, how big should the bubble be and where do I
> place the object? In the bubble or on top? This one seems to have a
> timer too, is there anyway to mechanically change the timing
> interval? It seems to only take a sight for about a minute!
>
> Assuming I was in an old DC-3 flying at 5000 ft, taking a LAN
> sight... What corrections would I apply.. I assume, temperature,
> pressure and altitude (pressure or density alt??) but would
> airspeed apply too? If so.. True Airspeed or Ground Speed? Would
> the correction be altitude only instead of Dip? If I have to
> correct for altitude, are there tables?
>
> Hoping you can help me shed some light...
>
> Thanks
>
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