Compasses are 180 degrees out

[IvanK]

You need to first determine the current magnetic heading from the Main compass. Once you have this set this on the directional Gyro.

Gyro precession is modelled so every 15mins or so you need to repeat the process. You also need to do this after hard manoeuvering.

To further complicate things acceleration and turning errors on the magnetic compass are modelled so you need to take this into account as well.

Magnetic variation is NOT modelled in COD