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There are some compass errors associated with the physical interaction
between a tiltable compass card, and a tilted geomagnetic field, such as
acceleration and turning (properly rolling) errors. These are abolished
with a bolt down sensor.
There are errors associated with channeling of the geomagnetic field
through ship locations offering easier passage ('magnetic permeability').
which vary with the relative angle between ships heading and magnetic North
and errors due to fixed magnetized components aboard. These remain.

If an autocorrection code can depend on a constant rate of change of
  heading during calibration, it can compute a deviation card and apply
  it automatically.

Tidal [straight-line] current would not vary this rate, but a brisk or
variable wind
might well disturb the turn with an unwarranted deviation being recorded.
    Your best strategy is obvious.

Brian W

At 10:21 PM 1/28/02, you wrote:
>I had a pair of magnetic fluxgate compasses for my Robertson
>autopilots.  The adjusting process was to put the system into
>a calibration mode and then proceed to steer the boat in a large
>360 degree circle at constant speed.  When the circle was completed
>you pressed a button and the electronics completed the process.
>
>-----Original Message-----
>
>Subject: Fluxgate compass
>
>
>In referring to Bowditch chapter 6 concerning compass adjustment, I would
>like to know if this applies to electronic fluxgate compasses.  Does anyone
>here have any experience with this or could refer me to other references?
>
>Thank you,
>
>Craig

Brian Whatcott
   Altus OK                      Eureka!

   

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