I was good with them the ones we had had a crt scope and a Battery pack. Only ones approved for aircraft since some idiot used one on the fuel tank probes and it did not end up well. I used to do a class on them wit coax, single wire twisted pairs etc, had rolls set up with faults in them for the tests, was pretty cool watching the light go on when the figured it out. Geve them a 5% tolerance on the distances.