35-odd years ago when I worked in telecommunications, one of my tasks was to train graduates on the equipment that we were commissioning, whch was electro-mechanical (TXE-2 crossbar system for those who know about such things). The kit was quite noisy in operation with a few tens of relays operating within a few hundred milliseconds and, with experience, we learned to be able to identify many faults from the sound the switching system was making. The grads just couldn't get this and wanted to insist that we went through the "specified" testing procedure with them so that they could find a logical path to the fault -- they just couldn't get it that a slightly different sound meant something like "terminals 6 and 9 on relay Q are reversed". This took at least 20 times as long! They did not seem to be able to understand that test gear is used to extend the senses and only needs to be used when the senses are inadequate. Talk abut frustration, knowing that we were training these people to be our bosses!

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Stephen