Ever hear of this speed detection system used by cops?

[ac97gt]

if you measure the yarn with a yard stick take care that you are accurate. you probably dont have one but i have seen them before, its like a cane with a wheel on the bottom and a little thing that looks like a tripometer, you can reset it and as you wheel the wheel (holding the "cane" handle) it counts feet. probably one of the most accurate ways to measure that kind of distance, but the yarn is also a good idea especially since you can bring it to court like you said. you just have to convince the judge you measured it accurately.