Ignore Mouse Rotation

Hi. I have an object Sky1 that rotates constantly and a camera with which I can look around. Also a compass that is inside the camera and should ONLY move with the rotation of Sky1. But when the camera is also moved, the compass rotates relative to the mouse movement and Sky1.

So I tried to remove the mouse rotation from the Sky1 rotation to set the rotation for the compass, but it just doesn’t work.

I hope you guys can help with a little example.