My son got a speeding ticket in Florida and was sure he wasn't speeding as he was driving beside a friend and my sons passenger was talking to the other car who said they were going the speed limit also but not ticketed. Anyway my son went on line to see if he could fight it and found a site that tells you how to fight a speeding ticket. He found one, don't know what it was, but it said that the officer is required to prove his radar was properly calibrated (they actually carry a log book for this) with the correct tuning forks with matching serial numbers to the radar gun. They didn't match but the judge found him guilty anyway. A real kangaroo court. The judge also said in his opening information if you calmed you were going slower than the speed on the ticket but were still speeding, only by a lesser amount you were still guilty.
But maybe you will have better luck in CA.