On Thu, 13 Mar 2008 21:09:24 -0700 (PDT), "
wrote:

On Mar 13, 5:39 pm, Bruce in Bangkok wrote:
... Perhaps you need to go to:http://www.steiner-binoculars.com/bi...arine/395.html
and read up on these glasses. They have a world wide chart showing
deviation in various areas. The maximum I noticed was 12.0 degrees.

The chart seems to indicate that the compass is "balanced" for the
specific area where the glasses are sold.

Good link. I don't believe that they are really talking about
deviation errors -- it's been a long hot day and beer has happened so
I could be wrong... I think they are talking just about tilt.
However, if that's true then the design is disappointing. It isn't
hard to make compasses that are much, much less affected by tilt.
I've got a couple of Plastimo Iris 50's that are Australian and I've
used them all over the Pacific with no serious problems. Tilt is
generally less than 10 degrees anywhere where the water is likely to
be liquid so, any sail boat compass will need to be designed to work
at angles much greater than those induced by magnetic tilt. I've even
seen flat compasses with an extra movement that lets the compass
magnet align itself with the Earths field in 3D. If the problem
really is tilt, and it is easy to tell by tilting the glasses up and
down, then the design is seriously flawed.

-- Tom.


I'm sure that you are right as the only thing that varies N or S would
be tilt. But they do show an illustration of how the needle is mounted
at angle depending where the glasses are used. In any event I think
the OP is looking for a needle in a hay stack if he wants 100%
accuracy from a compass. I used to swing aircraft compasses as part
of my job and never saw one that was 100% accurate on all headings.

I also think in real life that it doesn't make any difference. There
you are standing in a moving boat and taking a sight on two fixed
objects. You are just looking for the angle between the two objects.


Bruce-in-Bangkok
(correct email address for reply)