Is it possible to have a useful magnetic compass mounted atop a truck's dashboard, given all the metal and electrical fields? Close accuracy isn't required, just something that can provide the cardinal and ordinal points fairly accurately.

I'm also interested in pitch and roll indicators (bubble-level type devices that indicate the the degree of fore and aft and more usually side to side tilt through an arc, similar to those found on sailboats) suitable for mounting in a truck. Maybe a circular bubble level? They would be used for finding a level spot to park, not while the truck is in motion.

I know that GPS and my smartphone can do these things, but I'm old fashioned about having backups and not being reliant on electronics.

Thanks!

Magnetic compasses are routinely mounted at the helms of power boats, replete with all sorts of electronics and I understand they are "adjusted" to account for all the stray electrons. Sorry, not quite sure how that is accomplished.

Thanks. There are a lot of boat yards around here. One day I may go see what they say, and how much they charge to do the installation adjustment for me.

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:

Many newer cars come with a compass installed. My Subaru has one on the rear view mirror. It shows "N", "NW", "W", etc. It seems to be reasonably accurate for rough cardinal directions.

Boat compasses are corrected for the local field of the boat by using small magnets mounted around the compass. The boat is pointed in a known direction such as magnetic north, and the small magnets are adjusted to a position so that the compass reads correctly. Then the boat is pointed in another known direction and the process is repeated. This is iterated until the compass is more or less correct.

You can never quite get the compass to read absolutely correctly using this method. Consequently for precise navigation boats will have a "Deviation Card", which gives a small correction to be applied for each desired coarse. To sail a given course, the navigator first determines the True course, then corrects for Variation (same as declination for us landlubbers), which gives the Magnetic course. Then one must correct for Deviation (using the deviation card) to get the Compass course to be steered.

To remember the series of corrections "True" > "Variation" > "Magnetic" > "Deviation" > "Compass" there is the old salt's mnemonic "True Virgins Make Dull Companions!"

Years Decades back (1985 IIRC) I received a vehicle compass for Christmas. This was the type of compass you would expect to see in an aircraft or boat, but it was designed for a car/truck. I never had a vehicle worthy so it stayed in the box. It has the adjustments for magnetic deviation to account for steel in the car and instructions similar to what you would do with an aircraft on a compass rose.

Would you be interested in selling it?

That app looks very interesting. Unfortunately, my OBD port is occupied by my ScanGauge II (which I highly recommend).

What's the exact name of that app, or where I can i find it and its dongle?

Sorry, that will never happen.

The Torque app: https://play.google.com/store/apps/details?id=org.prowl.torque

The OBD II dongle is any generic BT dongle you can find. I have this one riding always connected for like 6-7 years already: http://www.amazon.com/Veepeak-Bluetooth-Scanner-Android-Diagnostic/dp/B011NSX27A - it's sitting flush in the port in my Subaru, so I made a tape flap to make its removal easier (sometimes it needs a reset, so I just pull it out and insert back).

This is may ball compass: http://www.amazon.com/EFORCAR-Compass-Navigation-Direction-Guide/dp/B00O9VGAFU