Brilliant code, hardware and instructions. Got up in no time! Please note the instructions in readme.md reads int pin to D7, while the code says 8

@rob42 said:

calibrate it by waving about in a figure 8 pattern? You need to do this very close to where you mount it.

I do not understand this. What is the expected advantage?
If you want to calibrate the device itself, you can do this anywhere.
If you want to calibrate the sensor output regarding the surrounding ship, you have to fix the sensor and rotate the whole ship.

Maybe the solution would be to add the device calibration to the ship calibration: First do the "figure 8 pattern" whereever you like. Store this as device calibration. Then mount the device and rotate the ship in circles. This adds the ship calibration. This is how calibration of every commercial fluxgate compass works.

I built and hooked up a signalk IMU as described in this repo. While my
boat is berthed I would expect it's magnetic heading to come out at
about 240 deg accounting for the declination for my area. If yaw is
measured in radians counterclockwise from magnetic north, I expect a
yaw (and headingMagnetic) value of ~ 2.09r ( (360-240) * (math.pi/180.0) .)

The headingMagnetic and yaw are consistently around ~2.91r

navigation.attitude: P:0.05910696 R:-0.04054242 Y:2.9157207

Additionally, I expect to see the pitch and roll varying from negative
to positive values as the boat bounces around slightly in it's slip.