It will be precise, certified and validated. As for irrefutable, if you think it's not, why not drive up there at 50 mph and when you get a ticket, decline the fixed penalty, go to court and plead not guilty. When it goes to trial, you can put forward your assertion that it was "just paced out...
I don't know how it works but I would imagine that the cameras are linked to a computer and each time a vehicle enters the first one a record is created with the reg no and time. This record is discarded after 3 minutes (2 miles at 40 MPH) unless the vehicle goes through the second camera in...
You, as the owner, are expected to use "due diligence" to identify the driver of the vehicle. If you fail to identify the driver then you can be prosecuted for it and you then have to prove to the court how hard you tried to find out who was driving. Simply saying "I dunno, could have been...