Hi tautech,
From previous posts Stuartambient seems to have an Amprobe 5XP-A which only has a 200mA input jack, so no 10/20A range.
Stuartambient: You would put one of the resistors in series with your circuit, then measure the voltage across the resistor. 1 ohm resistor will give you 1 volts per amp ( V = IR, V = Volts, I = current, R = resistance) and the .1 will give you 0.1 volts per amp. Since they're 5 watts capable, you can go up to about 2 amps on the 1 ohm and 20 amps on the 0.1. They will get pretty hot at those currents though.