Originally Posted by awsrock

You know those trailers that the police put up to tell you your speed -
anyone know how accuarate they are? I had to pull of my speedo needle this weekend so when I put it back on I went to test it out...said I was 4 mph too high, so I adjusted it and now I am 3? The second time was at dusk, so maybe that has something to do with it? Because I was sure that I compensated for it!

From memory, these things can vary between each other by a few mph

As far as I'm concerned though, 3 mph off isn't too bad so I might just leave it alone