speeding ticket by radar in Ga. help

What is the name of your state? Ga.

I was pulled over in Butts county Georgia for speeding.
As most people, when i saw the officer approaching, i let off the gas, I was passing the nursing home in which my mother was cared for for ALZ., i know the road well, if i had in fact been doing 50- it would have been like qualifing for nascar, and since familair with that road, i know that sometimes elderly people from the nursing home can "wonder off".
When he passed me, i glanced in rearview mirror, and he spun his car around and hit the lights, I first thought was wow, he just got a call, must be bad,to my surprise, he was pulling me over.
I stopped, and he came to my car and said i was speeding, i said no way, he says i clocked you doing 50 - in a 30. I said I was not speeding, he said something about the radar, and I said YES I WOULD LIKE TO SEE IT, AND went to open my car door, he pushed it closed, and said no i may not go back and look at it. he then took my license, and ins. and went back to write me a ticket, he came back, gave me the ticket, but said he dropped it from 50- to a 46, just to help me out ya know, then when i went home i notice he wrote originally 51- in a 30, he said 50 -n a 30, and then changed it to 46 in a 30, how do I REALLY KNOW WHAT HE CLOCKED ME DOING WITH THAT RADAR, THEN AFTER GETTING HOME I NOTICE HE WROTE I WAS DRIVING A 93 TOYOTA -BLACK IN COLOR, MY CAR IS RED.
Do i have any defense here, what exact words do i use if i want him to show proof of the certificate number when it was last calibrated,did he do it again after he issued me the ticket, and the fact about the wrong color car.
any help would be great.
I have never had a speeding ticket before.

Look up previous posts for GA. Car color issue is iffy, but may be a viable defense strategy, although not for the reason of incorrect ticket. Instead, the officer has to identify your car at trial, and he most likely would read from the ticket. Let this happen without objection, wait until prosecution rests, then ask for directed verdict because the car he described does not match yours (proove by showing registration). Officer cannot correct his own testimony - and you just proved it to be wrong. You can add that car model was not specified, so it's likely he clocked a different car.

That said, alone this may not be enough. Use discovery to find out answers to your questions, then make sure you ask for directed verdict if no proof of radar testing or calibration is presented. Visual speed estimate may be a problem regardless, hope officer is not going to use that in his testimony. If not, let prosecution rest its case and attack the radar evidence in direct examination and your own testimony.