Logic probe use

When I worked on logic boards, I used one all the time. For anything else, it looks pretty in the drawer. It detects logic levels, rather than voltages per se. IN TTL with its 5v power supply, a logic high could be 3v or it could be 4.9v, either one is a valid logic high, and the probe will not differentiate. When you want to know if a logic signal is functioning, that is all you need to know. Kinda like looking at a toggle switch - it is either on or off, and doesn;t matter how hard you threw the lever.

The logic probe is a great tool, but only useful for looking at logic signals. One cool aspect was they could pick up tiny little narrow spikes that were - back when - VERY hard to see on a scope.