Docs seem to think we would not understand many things so they just don't "waste" their time telling us stuff. And maybe we would not understand but then we are left to guess when not given explanations. When I had my first NCS, the doc tested from my knees down to my ankles. Never tested above my knee. I did not understand since I had NO pain below my knee, just from my hip down to my knee. When I asked him about only testing where I had NO pain, and NOT testing where I DID have pain, he said the nerve runs all the way down your leg. OK, but if below my knee is OK, then shouldn't the "problem" area be tested? At least that is what I was thinking.
He offered no further comment or information. I left thinking he did not listen to me or he did not know what he was doing.

When I had my second NCS/EMG with another doc, I asked him why the previous doc did not test above my knee. I got a comprehendable explanation and felt much better about the process. When he did the EMG part of the test, he did stick the needles in the muscles in my upper legs.

I have learned to press for an answer until I get something from them that I can understand at least partially.