But a magnetic compass, I've found, is better for
shooting bearings for things like range cards. To sight a bearing on a vista you rely on the lanyard as well as two small white lines at the top and bottom of the display. By holding the vista in front of you, lining up the white hashmarks, and then selecting "project waypoint" the vista will give your a bearing to target. This IMHO, is easier to do on a magnetic compass. The sighting notch above the mirror is easy to line up with the lanyard, then it's a simple matter of putting the red in the bed.
It's hard to explain on the interweb.