What's the minimum distance a state trooper has to follow you to accurately pace you?

Question

I know some troopers use things like VASCAR to calculate speed but if the trooper is strictly pacing you, how far, or for how long do they have to pace you to get an accurate speed?

Answer 1

Not sure if its the same in the states, but here (In Canada)  The speedometer in a police vehicle is not considered a reliable method of "clocking" another vehicle.

If you have recieved a speeding ticket and were informed by the trooper that the method used to determin your speed was to "pace" your car, I think you have a pretty good case and providing that information to a judge may get you off the hook.

Answer 2

all the have to do is bang and the got your speed on a radar gun hehe bang-bang hehe :- )