Move the phone and the shape stays where it was. A 9:16 rectangle at half your screen height shows this far better than a dot: you can see translation and roll at the same time, and the edges make small errors obvious.
Turn and tilt the phone for a few seconds after starting. The ring at the centre fills as the rotation model is learned and turns green when it has enough.
Tap anywhere to recentre.
Rectangle: — × — px.
Learns online from the raw gyroscope channels — no axis labels, so a mislabelled channel cannot put the correction on the wrong axis. Set Strength to 0 % to see what it is doing.
Settled offset from a 0.03 m/s² residual: 10 mm.
World is correct: the rectangle stays upright in the room and swings around as you roll the phone. Screen ignores roll entirely, which isolates translation while tuning.
Roll axis: detecting.