1.1°
The scan that bent as the head turned
Per-frame geometry was fine at 12.7 mm plane fit, yet the accumulated scan curved. Four plausible causes, including the speaker magnets next to the IMU, each fell over when measured. The answer came from diffing the app’s own export against its render: a 90-degree roll meant to align the depth grid to the camera had been applied to the world projection. Static-wall error 14–20° before, 1.1–2.1° after, verified to 0.009 mm.