If you "plug in" an analoge meter in the "wrong way round" you should'nt be using one
One BT engineer at the Model Railway Club one night was testing the O gauge layout for a fault. He found loads, diodes the wrong way round and the like. Until someone pointed out he had the leads plugged in the wrong way round...
Aren't you supposed to also affix a shirt-circuiting bar between the positive and negative live rails immediately after testing that the track is indeed dead - leaving it in place until the work is completed???
In some ways, Windows XP was equivalent to the 1938 trains - A very long life, and the Windows Vista was the equivalent of the Short-lived 1983 trains - withdrawn prematurely.