Guess My Speed and Give Me a Ticket, In Ohio
quall writes "The Ohio Supreme Court has ruled that police may estimate your car's speed and issue a ticket if they believe you were speeding. The hearing threw out a radar gun as evidence because the officer was not qualified to use it, but apparently his guess was good enough. If you make your way into Ohio, I suggest driving 5mph under the speed limit because this leaves little room to dispute your ticket in court. The only chance you have is if the issuing officer decides to skip your hearing."
I wonder whether the court would also accept a driver's own GPS log as exculpatory evidence.
The article indicates the driver was going about 15mph over the speed limit. I'd say that was relatively easy to identify by sight. So what the majority said, which is in fact "given the totality of the circumstances", such an officer's testimony may be held to be credible. If you can show at trial that the officer has borne you a grudge since high school, that may well be another story. And of course it's not in front of a jury - its $50, for crying out loud!