I have an 8 directions electronic compass in my auto-dimming rear view mirror. But in practice I'm using a simple cheap ball compass on my dash for 16 years. When mounting it - put your car into a known direction first and move the compass mount around on the dash (before sticking it in a permanent spot using self-adhesive pad) to find a location where it shows a correct magnetic direction to you. That's where all of the anomalies are self-negating. Surely it will be off by a bit anyway, but for a quick direction pick that's not crucial at all. Also the ball shape gives you an immediate pick on the pitch and roll data as well. Nothing super precise, just a general sense if it's significant or dangerous (just make sure you affixing the mount on a level surface, mine has a pitch adjustment though). Keep in mind though, that when moving, the pitch/roll data will be affected by the vehicle acceleration forces as well, because the device is gravity based.



In the recent time, I've started using my Android phone on the rural road trips as a dashboard supplement. The Torque app has plenty of fantastic features for the car driver, including the arbitrary dash design, which has the roll and pitch gauges as options, the compass, fuel economy meter, and plenty more. It's also connected to the OBD-II blue tooth dongle in your car's OBD port. So the amount of features depends on your car's computer as well. Here is the screenshot of my current travel dash, which I've designed myself: