Compass Interference
Also called: compass error, magnetic interference, deviation, metal near compass
Steel, magnets, and electronics near a compass pull the needle and give a false direction. Keep it clear when you take a reading.
- Type
- Compass
- Common culprits
- Rifles and knives, vehicles, belt buckles, phones, radios, magnets, and power-line transformers
- Safe distance
- A few feet from small steel items, much more from a vehicle or large metal object
- Also affected
- Needle can reverse polarity if it sits against a strong magnet
- Used for
- Hiking & camping, Hunting, Fishing & boating
Safety: If you are a hunter, put the firearm down first. Keep it unloaded with the muzzle pointed in a safe direction, and never lean it where it can fall. Do not hold a firearm in one hand just to keep it away from the compass.
What it is good for
- Spotting why two readings disagree.
- Taking a clean bearing at a trailhead, stand, or boat.
Where it falls short
- Mineral deposits in the ground can also affect a needle, and you cannot always tell.
- A dead-looking compass may just be a reversed needle, which can sometimes be fixed by a service shop.
Tips
- Step away from the truck before you take a bearing, and hold the compass out at arm's length.
- Take a second reading at another spot, and compare it with a landmark.
- Store the compass away from magnets, speakers, and phone cases with magnetic clasps.
Works well with
- Baseplate Compass: the compass most affected when held close to a pocket.
- Taking a Bearing: the reading that interference spoils.
Field notes
A needle is a tiny magnet, so any larger magnet or piece of iron near it pulls it off north. Many bad bearings come from standing next to a truck or holding the compass against a belt buckle or phone.
Related guides
Numbers here are typical, and values such as magnetic declination change over time and place, so check a current source such as NOAA or your map's legend. Practice near home before you rely on a skill far from help, carry a paper map and compass as a backup, and tell someone your plan. Rules on electronics, land access, and trespass differ by state; our state resources directory links to each state's official regulations. Want a step-by-step guide? Read Trail Navigation Basics.