Couldn't you say the same of drug testing spectrometers etc? The end operator of the equipment has to appear in court to testify to the proper operation of the machine. [0]

[0] Unless the defendant waives that right and stipulates to the prosecutor's statement about the machine.

This literally occurs; one of the reasons that the drug testing lab is usually somewhat local. The prosecution called the individual who ran the test as a witness, and he had clearly been called for similar things many times before.