Originally Posted by JohnJ80

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When you are being followed by a car that is going at the same speed you are, that “target” will drop off the display. The Varia Radar measures differences in speed to determine if something is behind you and approaching. It cannot know about something that is the same speed as you are. If you haven’t seen this already, eventually you will. But obviously, if you were to presume it is accurate all the time, then if you saw the Radar telling you that there is nothing behind you and you were to make a left turn right in front of a trailing care - well, would be ugly and potentially fatal. If you presume that the Varia Radar replaces your mirror, you are asking for it - bad to make that presumption.

That said, once you know this and “trust but verify”, then it is indispensable. .....