But in game are modeled the 1940 deviation magnetic, or the Needle on Compass point 10 degrees for left off real (earth) North. Take this into account when plan you flight routes (the in game map provide "pencil/king pin, eraser, ruler and protractor in Map Tools).
The P-8 compass is difficult to see since is behind the control column (workaround, TrackIR, Freetrack, NewView, HAT+JoyToKey, 6DOF on mouse), and difficult to read since his scale seems inverted.
And the DG get uncalibrated after some maneuvers.
Take a look:
After this procedure use the command "Glance at dashboard" to easy check the DG.
As "Rule of the Thumb" 10º is fine for typical fighter flight across the Channel on CloD map, and simplifies players compensate readings (just add 10).
If one go bombing London in a He 111 leaving Tramecourt, a more precise value is welcome. Desastersoft KG 54 campaign comes with a adjusted 8º (PDF) protractor.