No orientation readings. The overlay can't follow the phone. In Chrome, tap the icon left of the address → Permissions → allow Motion sensors, then reload.
Point your phone out of a window to see where the sun travels during a period or a season. If the band crosses open sky, the room gets sun.
Uses the camera, compass and location. Nothing leaves your phone.
Highest path Lowest path Sun can be here
In Shade check the band turns stays orange where the camera sees open sky and dark and hatched where something blocks it.
North is read from the compass once at start (corrected to true north like Google Maps) and then locked: turning the phone is tracked by the gyroscope only, so metal and electronics nearby can't make the overlay drift. Δ in the bottom bar shows how much the compass disagrees right now. If the overlay looks shifted, tap Re-align N near the window, or better, calibrate with the sun.
If the overlay is shifted sideways, drag this slider. On a sunny day, Calibrate with sun is exact: point at the sun and tap Set, and north is locked to the sun instead of the compass.
Across the long side of the camera image. Calibrate once: aim at a distant object, then turn until it reaches the edge marker.