When I put the device horizontally on a desk, I don't expect autorotation to be triggered, even if the desk is not perfectly flat. When I then rotate it around a vertically-enough axis that is perpenicular to the screen, the autorotation triggers every 90 degrees, showing how the desk is not precisely horizontal. It obviously misses some hysteresis-style thresholds.
When I put the device horizontally on a desk, I don't expect autorotation to be triggered, even if the desk is not perfectly flat. When I then rotate it around a vertically-enough axis that is perpenicular to the screen, the autorotation triggers every 90 degrees, showing how the desk is not precisely horizontal. It obviously misses some hysteresis-style thresholds.