Their primary use is for phone/alarm wires. The second part of the set is the "wand". (the inductive receiver that picks up the tone) We put the tone on the wires and with the wand we can find the wire 500 feet away, in the middle of a bundle without having to physically follow the wire through all the ceilings. Tone won't go over shorted wires, thus the continuity setting. If the wire is shorted together we put the second clip on ground. The telco plug is paralleled with the clips. Plug it in a jack and you can pick up the tone at the punch block in a heartbeat.
I've never been able to make it work on shorted BX and if you ever put it on an energized (120v) wire ... you'll know you made a mistake.
