My first thought was, someone who doesn't know the science and needs it explained, e.g. Captain Brass. But then I remembered that CSI often annoyed me with its abundance of "As you know, Bob" speeches where the scientists explained basic science to other scientists who already know it. That's kind of unavoidable in TV, but in a book you have internal-viewpoint narration so you don't need the stilted lecturing. So maybe it's better to be in the head of the scientist performing the test, so it can be explained through their thoughts.