Sensor noise

Sensor noise is the random jitter and small systematic errors in every real measurement: no thermometer, gyroscope or accelerometer reads exactly the truth. Random noise averages out if you take many readings, but a constant bias (a gyro that always reads slightly high, say) does not. The trouble really shows when you integrate, adding up readings over time to get something you can’t measure directly, like turning rotation rate into heading or acceleration into position. Every small error gets added in and never cancels, so the estimate drifts further and further from reality. That’s why systems correct a drifting sensor with an independent one, such as a magnetometer or GPS.