random accuracy in SensorEvent.accuracy

most people won't bother much about the accuracy of the reported sensor data, but for the company I'm working for this information is crucial. on Nexus 5 and Galaxy S4 (and possibly some other devices) we noticed that the value stored in the SensorEvent (given via SensorEventListener.onSensorChanged) is seemingly random (ranging from -100 to +100, instead of holding one of the SensorManager.SENSOR_STATUS_* constants.

we only saw this happen for sensors of type
Sensor.TYPE_ROTATION_VECTOR

this was reported and fixed by google for android lollipop: https://code.google.com/p/android-developer-preview/issues/detail?id=1453

workaround for older versions of android is to only use the accuracy given via SensorEventListener.onAccuracyChanged, which always reports the correct accuracy so far.