Running in neutral, all aggregates are strong. This is valid for engines and also for generators. This idle running does not refer as much to the RPMs, but to the strain, which can be quite high, even at idling speed. With the tester shown above, you are able to measure the voltage and the current delivery under such strain.
The thinner cables with two terminals (red on plus and black on minus), are actually, always necessary. These can both be clamped onto the battery, but also to any other point of the circuit, to measure, e.g., the drop in voltage. If both are clamped to the battery, and the larger terminals with the thicker cables (red on plus and black on minus) as well, you can, using the lever on the left, increase the strain by lowering the resistance between plus and minus, and at the same time, show both the current and the voltage.
In addition, there is also the current measuring clamp with which you can measure the current at any other place. 06/09