Compass

[Puddintane]

I have bought several different compasses, that are made for automobiles. No matter the location I install them, they fail to show the proper direction. Even if the the car is sitting still it's never correct. If I remove them from the car they seem to work properly. I've tired to use them in two other cars and they all show incorrect directions. I only take one compass in the car at a time. PLEASE HELP (Thanks)

[heathfield]

The steelwork in the body of the car is distorting the earth's magnetic field, causing the compass to point in the wrong direction. Any magenetism in the steel will also add to the error on the compass. Almost impossible to correct. (See 'compass correction' for ships on Google). Unless you're planning to cross the Sahara, a dash-mounted car compass falls into the same category of usefulness as furry dice.

[Ethel]

It is caused by the amount of metal in the car causing the compass to give a false reading.

I don't know if anything can be done to improve things though - unless you spend an awful lot of money on a specialised one.

[Mortartube]

Unfortunately, the amount of steel in a car will cause dramatic deviation on a traditional magnetic compass.I assume that we aren't talking about electronic compasses. Ships have the same problem and the deviation is corrected by special magnets placed near the compass (Look at old ships compasses in their binnacle and you will often see two spheres (one red, one green) on the side. This corrects the error which was previously worked out and entered on a "Deviation Card".

[cascarelli]

Yes, its the magnetic fields of the car affecting the compass. One (albeit more expensive) solution is to use a GPS unit. Even the cheaper hand held models will have a compass bearing built in (calculated from the relative positions of satellites). It will also give you a lot more information (average speed, fastest speed and, obviously, your position etc etc).

[Puddintane]

Thanks to all that answered. You have been very helpful.