Once i t reaches 50 +/- miles it becomes very unreliable. I once had a situation where I had a reading of about 30 miles. As i was looking for the nearest station the miles started dropping like a rock. In the course of two +/- miles the reading dropped from 30 to 15...12...8. This was in a E39 5Series. Scared the livi'n $hit out of me...............