Drop off to Pick up Radio

To illustrate what RAMConsult said, consider if your pickup and dropout point were set to exactly the same value (say 135V for overvoltage on a nominal 120V system). If your voltage increased to right around 135V with a slight jitter in magnitude, your relay would be picking up and dropping out as the value teeters on the high or low side of 135 volts.

But if you set your pickup to 135V and your dropout to 130V, your relay would pick up at 135 and stay active until the voltage level dropped below 130V, at which point it would release. The other thing to consider is whether there is any defined time delay associated with either the pickup or dropout values, so that the measured value has to stay within the range for some time period before the relay actually operates.

Again, it's part of learning the art & science of protective relaying, as was said.

When you drop the radio off you need to pick it up again!

And

No guys not OT. Its in total response to the title!