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Alex, I find myself wondering:
 If  a dip meter is a useful instrument, why were they neer popular and now
extinct?

To which I have to suppose they serve no useful purpose in marine
navigation, which leads me to suggest a reason why this might be so.

At sea, well away from land and in theory surrounded by uniform water--at
least, surrounded by enough of it to reach the horizon--the dip correciton
is usually made by compensation for barometer and temperature, yes?

And the inaccuracy in this is often from changes in temperature, i.e. from
being on land shooting a horizon over the water, where tempearatures in the
air will differ. This was gone into in some depth, I think two years ago.

So let's look at what a dipmeter is measuring. It is *not* measuring the dip
in the direciton where you are taking your sight. Rather, it is measuring
that dip, and the dip behind you--which may or may not be the same--and then
averaging them.

If the dip behind you differs from that ahead of you, you've simply
compounded errors and wasted time doing so. If the dip in both directions is
the same...I suggest the standard compensations for temperature and pressure
are close enough to be enough.

So then, here's my hypothesis for you:
 Standard compenstaions under standard conditions (uniform air mass) are
significantly equal to the results obtained from a dip meter, AND a dip
meter may in fact introduce more errors while consuming the navigators time
and energy.
 Therefore they were never popular and have no role in routine marine
navigation. And, they will add nothing significant to the precision of it
today.

Your thoughts? Surely, there's a reason why they were never popular, and
researching them is like looking for hens' teeth.

   

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