Probably only people of my vintage would remember what a rheostat was. It's what we used to control the volume on our superhetrodyne receivers. And those are ....radios. Many of these volume controls were actually numbered.
There are those who control their emotions much like the numbered knob above controls volume, very seldom ever reaching the highest output. Sometimes they can be quite frustrating because their reaction can be very difficult to gauge. Then there are those whose volume control is always set at ten and just turn emotions on and off.
Me? I am a firm believer in holding something in reserve and try to keep my volume set at around 1. I'm leaving 10 for the hopefully never to come 'big one'. Unlike Donald Trump who is another who seems to operate with the dial on maximum.