Compass Calibration Guide
Learn how to calibrate your phone's magnetometer using the figure 8 method to fix inaccurate compass readings and improve GPS accuracy.
Why Does the Compass Need Calibration?
Your smartphone uses a tiny chip called a magnetometer to measure the Earth's magnetic field. However, this field is very weak and easily disrupted by everyday objects. Common culprits of magnetic interference include:
- Phone Cases: Cases with magnetic clasps, MagSafe accessories, or metallic wallets.
- Electronics: Laptops, speakers, microwaves, and power cables.
- Vehicles & Buildings: Being inside a car, an airplane, or a building with a heavy steel frame (rebar) can completely distort the magnetic field.
Even when perfectly calibrated, remember that your compass points to Magnetic North, not True North. If you are navigating with a map, you will need to account for magnetic declination to reach your correct destination.
Checking iOS Compass Accuracy
If you are using an iPhone, Apple's Safari browser sometimes provides a specific property called webkitCompassAccuracy. If this number is high, it means the sensor is highly disturbed. The goal of the figure-8 motion is to lower this number to an acceptable range (usually under 15 degrees).