[FiscusFish]

I was sure that for it to be valid there are rules about the angle they can get you at. A car coming straight at them would require a different calculation from one targeted at a 20 degree angle away on the other side of the carriageway.

"Slippage" (where the point targeted on the vehicle moves and affects the reading) would also be more likely with a wider angle.

Perhaps one of the resident coppers on the board will come along and give us a view?