Digital Compass
The Untangled Labs Digital Compass uses your device's built-in magnetometer and orientation sensors to display a real-time true-north heading with automatic magnetic declination correction. Magnetic declination — the angle between magnetic north and true north — varies by location and changes over time. The tool fetches your GPS position and applies the correct declination value from the NOAA World Magnetic Model so the heading always points to true geographic north, not magnetic north. Features include a smooth animated compass rose, bearing lock mode to hold a fixed heading for repeated measurements, a figure-8 calibration routine to reduce sensor interference, four-zone audio beeps for hands-free alignment workflows in the field, and a manual fine-tune slider for environments with local magnetic interference. On iOS devices, the tool detects whether iOS is already applying internal declination correction via webkitCompassHeading and avoids double-correcting. The compass works on Android phones and tablets, iPhones, and iPads in any modern browser that supports the DeviceOrientation API. Sensor permissions must be granted when prompted. Free GIS tool, no account required.