How the AR compass works. The device magnetometer provides a magnetic heading. Magnetic declination for your exact latitude and longitude is computed from the World Magnetic Model 2020 spherical harmonic expansion to degree 4, then added so the overlay shows true north, not magnetic north. Each direction occupies 22.5 degrees, and the 16 zone boundaries are offset by 11.25 degrees so that North is centred rather than edge-aligned. Sensor accuracy is read from the browser and displayed live, so you know when to trust the reading.

How colour is read. The centre 36 percent of the camera frame is sampled, converted from sRGB to HSL, and a hue histogram identifies the dominant family. That hue is then matched against the Vastu colour rule for the zone you are facing, using the classical elemental logic: fire zones want warm hues, water and air zones want light cool hues, earth zones want earthy warm neutrals. Lightness is also weighed, because very dark colours are heavy and belong in the South and South-West, while the North-East must stay light.

Honest limits. Phone magnetometers are typically accurate to two to five degrees and drift near metal, lifts and steel structures. Tap Set North while pointing at true north to calibrate away any constant offset. Colour reading depends on lighting, so scan a wall in daylight if possible rather than under a warm bulb.