i read about a glitch in the software where it will calculate the speed based on where you were when ou last turned the unit off and then turned it on after moving. it sees a large distance moved in what it thinks is a small amount of time. in particular, i heard of a reported speed of over 6000 miles/hr for a guy that was hiking. like everything you hear in life, it is up to you to decide whether or not you want to believe what the gps tells you.