I was ticketed 130 on the 401 but an OPP officer that I was following.

He did not overtake me...I was actually behind him after he passed me! I intend to challenge this and that I was going the "normal flow of traffic" and that his estimate of my speed is unreliable.

Can the officer claim he "clocked" by reference to his own speed? I intend to challenge his estimate of my speed on the basis that a visual reference, in rearview mirror no less, and the variability of a speedometer provides an unacceptable margin for error, especially given that I am right on the bubble for 4 points. The officer stated that he reduced it by a few km, but didn't specify what my speed was, so I sense that there's a rounding factor going on here if he can't affirm and exact speed.

Whats the actual burden of proof for a non-radar measure?

Police do have rear facing radar, I got nabbed last year, 124 behind him, 119 after I passed him. I'm sure the people here can offer more insight such as disclosure etc...

Pacing is quite common, which he probably used.........Search on here for posts and question regarding this.

BEN wrote:Whats the actual burden of proof for a non-radar measure?

Police cruiser speedometers are calibrated pieces of equipment and are accepted in court as an accurate measure of a vehicles speed through pacing. What an officer needs to prove the charge is to state how long he was following you for, that he maintained a constant distance and what he observed his speedometer to read.

Obviously, the limitation of reading a speedometer is that it's analog, not digital like a radar, which is why officers often round down, to remove the error. The margin of error is not in the device, it's just in the observation. There's nothing wrong with that as long as they can say it was "at least" as much as they charged you with. So if it was around 132...133...135 or something like that, but definitely over 130 and he charges you at 130, it will stand up.