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Let's make that very clear:  One should check IE every time a sextant is
used, not for each sight taken at that time of use.  I usually check
(better, *determine*) IE both before and after taking sights. Invariably
IE is the same, even on a Davis plastic sextant.  But if it ever were
different, that would be a flag that IE might have drifted throughout my
run of sights.  Then I'd have to look at how much it had changed (a
tenth of a minute or two is not a lot to worry about, a few minutes
definitely is) and decide if that drift put my observations in doubt (on
the other hand, even a position thrown off by IE drifting a minute or
two might be a whole lot better than a DR!).

I think all this comes under the topic of "getting to know your
sextant."   Love it, cuddle it, hold it, take sights with it, check it.
Soon you'll have a feeling for it's peculiarities and behavior well
beyond any words of wisdom from this list.

Lu Abel

Fred Hebard wrote:
> Right,
>
> One needs to check IE each time the sextant is used.  But one doesn't
> need to ADJUST IE to zero each time.
>
> Fred
>
> On May 8, 2006, at 10:45 AM, Red wrote:
>
>> Greg-
>>  Even with a better sextant, it is "proper" practice to check for
>> IE every time you use the sextant. I've seen IE hold at zero for a
>> zero, even with changing temperatures, but all it takes is one
>> bump, one slip, and then your sights are down the drain. Far more
>> "professional" to check it every time so you know it hasn't
>> changed, instead of assuming so.
>>  The plastic sextants are supposed to be less stable with
>> temperature change, so that taking one from a warm indoor home out
>> into cold air, or taking one and leaving it in hot sunlight, etc.,
>> all can cause thermal changes in the frame, which bring changes in
>> the IE.
>>
>
>

   

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