Just for clarification, “reasonable doubt” would not be the test for this type of case should you actually appear in court. You would basically just have to prove to the judge’s satisfaction (read: completely prove) that the reading was measured incorrectly or that some procedure wasn’t followed. Unfortunately unless you are pretty savvy about the law, most judges are not quick to find this sort of thing in your favor. Little technicalities don’t mean you’ll get out of it, and they know you are basically not going to file an appeal because it’s way more expensive and time consuming, negating the value of getting out of the ticket.
I clerked for a county court and watched stuff like this happen all the time. You are definitely fighting an uphill battle if you take this stuff into court.