I am using a digital multimeter to monitor AC currents through a circuit that dims fluorescent lamps. I need to have a steady reading of for example 70 mA. I find that with the digital meter the readings keep jumping about. I have an AC ammeter with a needle but the scale is up to 5 amps. What size shunt would I need so that I can easily have readings from about 50mA up to 150mA?