Just bought a 2000 SilveradoLS. Has a temp/compass mirror. Truck did not come with a manual. I think the display is flakey. If i hit temp or compass, both displays come on. Each will not come on separately. Also, a little light that says "cal" comes on, and it goes trough n,s,e,w. Is it self calibrating? Any ideas, links or posts that explain user options or operation is appreciated!