Let me get this straight... the officer SHOWED you the lidar gun and it said 69, but then wrote you a ticket for 73? Wow. I don't understand that. I think I would argue that as being indicative of his credibility. That seems pretty hokey to me. To bad you didn't snap a picture of the lidar reading with your cell phone camera or something.

As for your fine, I believe you are about to get a runaround job that CA does pretty regularly. You were charged with VC22349a:

22349. (a) Except as provided in Section 22356, no person may drive
a vehicle upon a highway at a speed greater than 65 miles per hour.
At 73, you were only 8mph over the speed limit that you were charged with violating. However, if you consider the 55mph posted speed limit, then you were 18 mph over the limit. So, given the jump in fines occur at 16mph over, you were charged with 8 over, but you will likely be fined for 18 over. This is wrong.

Why do CA cops do this? Because if he charged you relying on the speed limit of 55mph, he wuold have had to write you under VC22350 and all the speed trap laws would come into play. This means that the cop would have to present speed surveys that prove the 55mph speed limit was justified. So, the cop charges you with the easier to prosecute offense (22349) but the court fines you based on the posted speed limit as if it were a 22350 charge.

This presents an interesting opportunity. If I were in your situation (and the fine was based on 16+mph over), I'd show up to court and ask for a dismissal if the cop didn't present the speed surveys. When the judge points out the obvious "22349 does not require any justification of the statutory limit", I would reply that the evidence shows that the state is really charging you with 22350 based on the amount of the fine. Therefore, speed trap laws ARE in play and the officer must produce the speed surveys.

It would be really interesting. I believe the worst case scenario is that the judge lowers the fine to the under 16mph rate.