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.

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)

On Fri, 14 Mar 2008 15:58:49 +0700, Bruce in Bangkok
wrote:

snip

In any event I think
the OP is looking for a needle in a hay stack if he wants 100%
accuracy from a compass

snip


It doesn't seem he's looking for 100% accuracy at all. The issue here
is whether we should be surprised at the Steiner's demonstrated
errors. There is a tendency to be appalled at the performance of such
a high quality instrument. But do our prior expectations come from
some source other than the high price?

Chuck

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On Mar 13, 10:58 pm, Bruce in Bangkok wrote:
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.

I don't know how the OP intends to use the compass but 7 degrees is a
lot of error. More than twice what I'd expect from a well corrected
compass. Keep in mind, with deviation, the error will be between
headings so the angle between your two objects could be 7 degrees off
in this case... Good thing he's got a GPS.

-- Tom.

On Mar 14, 8:16 am, " wrote:
... Keep in mind, with deviation, the error will be between
headings so the angle between your two objects could be 7 degrees off
in this case... Good thing he's got a GPS. ...

And, while I'm in the bad habit of replying to myself and just for the
record: you can't get a fix with just the angle between two objects
and no azimuth. The angle only gives you a circle of position (or to
be fully correct two possible circular arcs of position except where
you have a transit and it becomes a line of position). With just
angles between objects you need three to get a 2d fix (unless you have
transits where you only need two). But you knew that

-- Tom.

On Fri, 14 Mar 2008 11:42:16 -0700 (PDT), "
wrote:

On Mar 14, 8:16 am, " wrote:
... Keep in mind, with deviation, the error will be between
headings so the angle between your two objects could be 7 degrees off
in this case... Good thing he's got a GPS. ...

And, while I'm in the bad habit of replying to myself and just for the
record: you can't get a fix with just the angle between two objects
and no azimuth. The angle only gives you a circle of position (or to
be fully correct two possible circular arcs of position except where
you have a transit and it becomes a line of position). With just
angles between objects you need three to get a 2d fix (unless you have
transits where you only need two). But you knew that

-- Tom.
Well, normally when you are doing it you take the angle between two
points a known distance apart...

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

On Mar 14, 4:48 pm, Bruce in Bangkok wrote:
Well, normally when you are doing it you take the angle between two
points a known distance apart...

That still gives you an arc of position, not a fix.

-- Tom.

On Fri, 14 Mar 2008 11:16:58 -0700 (PDT), "
wrote:

On Mar 13, 10:58 pm, Bruce in Bangkok wrote:
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.

I don't know how the OP intends to use the compass but 7 degrees is a
lot of error. More than twice what I'd expect from a well corrected
compass. Keep in mind, with deviation, the error will be between
headings so the angle between your two objects could be 7 degrees off
in this case... Good thing he's got a GPS.

-- Tom.

I had assumed that he was using the glasses to measure the angle
between two known objects as is normal with a hand bearing compass. In
which case whether or not the glasses were reading the correct
magnetic heading is irrelevant.

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

On Mar 14, 4:41 pm, Bruce in Bangkok wrote:
... I had assumed that he was using the glasses to measure the angle
between two known objects as is normal with a hand bearing compass. In
which case whether or not the glasses were reading the correct
magnetic heading is irrelevant.

I don't understand what you are saying. Bearing compasses are almost
always used to get azimuths which are then often plotted on a chart.
They have to read properly to work. If you just want to know the
angle between two objects you don't need a compass at all. For small
angles you can get within a few degrees just siting over you
outstretched hand (each knuckle is about 3 degrees). A cross staff,
peloris, kamal, sextant etc can be used for larger angles. If the
magnetic heading is irrelevant why have a magnet compass at all?

-- Tom.

Bruce in Bangkok wrote:
On Fri, 14 Mar 2008 11:16:58 -0700 (PDT), "
wrote:
I don't know how the OP intends to use the compass but 7 degrees is a
lot of error. More than twice what I'd expect from a well corrected
compass. Keep in mind, with deviation, the error will be between
headings so the angle between your two objects could be 7 degrees off
in this case... Good thing he's got a GPS.

I had assumed that he was using the glasses to measure the angle
between two known objects as is normal with a hand bearing compass. In
which case whether or not the glasses were reading the correct
magnetic heading is irrelevant.

This is only true if the error is constant. For example, you don't have
to be concerned with variation if you're only considering the angle
between two objects. However, if, as is apparently the OP's case, the
compass has deviation that changes with heading, then the computed angle
will be faulty. The reported data implies that the angle could be off
by more than 8 degrees, which makes it hardly worth plotting.

Traditionally, a horizontal sextant sight is taken. This can give a
high degree of accuracy. Until recently, such sights were the primary
technique for positioning buoys.