Roll gyro?

[Jkoonce128]

Looking for a little knowledge here. Yesterday I was flying VMC at 10K with about a dead 5 knot headwind. 430W was feeding the GRT and the GRT was controlling the TruTrak RV 10 AP. Very stable and confirmed with Foreflight on an iPad. The heading displayed on the PFD screen was more or less constantly rolling with fairly large errors. The magnetic compass confirmed no roll present at all.
I went to setup for the AHRS and down to the Magnetometer data. That was stable and consistent with the Magnetic compass. Just next to that was the "roll heading" which was consistent with the roll being displayed on the PFD.
What is a roll heading ? Since my magnetometer was dead on I don't see how a calibration will help. I have dual AHRS and the unit displayed that all data was valid. I'm hoping this is a setting problem but am mostly wondering what the roll heading is. I thought the magnetometer was the source of heading info to the unit.

Thanks in advance,

John Koonce
RV 10 N78MU

[GRT_Jeff]

Do you mean the compass heading was constantly changing, or the PFD was showing your wings weren't level?

The magnetometer data is not directly displayed. It's used to continuously align the yaw gyro. If there is a disagreement between the gyro solution and the magnetometer data, the compass heading may slowly change to match the magnetometer data. Large disagreements indicate magnetic interference.