I saw that, but I still don't see how that works in a trial. Said evidence will need to be introduced in court. When the witness tries to be cute by giving a vague answer, can't the defense just ask the witness to explain further?

This is entirely false. For gods sake, you have to put lab technicians on the stand for cross examination when they test your blood.

For something like this, a report gets written, and the person who wrote it gets cross examined.