I think the gun clocks speed iteratively and gives speed and distance- it can generate 4,5 speeds as the car approaches. He may have had you at 73, but the last reading that was locked in was the 69 (after you started slowing)
I agree with you... but the cop provided evidence to the contrary. Typically, cops will NOT show you the lidar reading. They will simply testify to it. But since he showed it, he impugned any testimony of 73.