[RBHoge]

Here in Murfreesboro, Tennessee, the Police department has two or three trailer mounted "Speed Check" devices. As one drives by the lighted display announces "Your Speed" as you drive past.  I have been known to circle the block a time or two to verify my speedometer as I drive through the radar trap. So far my bullet is quite accurate.

Another choice is mile markers on county roads and a watch. it takes two minutes to drive one mile at thirty, and one minute to travel one mile at sixty.  To be more accurate one can do the math, or get a copy of "Larry Reed's Rally Tables."