I use newer versions of all of these at work daily. The first one is a “megger”, it puts out a really high voltage, low current. We use it to check for grounds in motor windings and feeder cables. A ohm check with a multimeter most times won’t show a ground if the insulation has broken down, but that high voltage will leak to ground and show it with the megger. We still use the old hand crank style occasionally, but we have a digital one now that you just push a button.
