Why bother with compass card?....because half the aircraft i have flown have some compass headings 5-10 degrees off.
For instance fly west set di/compass, fly east and its off several degrees.
Or compass/di perfectly aligned just before turn point, then on checking after turn 5 degrees off.
So what do we do ground aircraft until it is reswung at £xxx cost..or do clubs just put up. I have known aircraft go through CofA's and still have major/same errors.
At least basic training aircraft compasses should be test swung every six months with all the bashing they get.
With radios on and pitot OFF.