Martindale cm57 600a ac true rms trms clamp multimeter martindale cm57 p the martindale cm57 is a pocket sized high performance ac clamp meter with ranges for ac current ac voltage dc voltage resistance with continuity test as well as capacitance frequency and a diode test its true rms measurement ability ensures reliable readings even with distorted waveforms that are often caused by modern lighting and power supplies the cm57 s smart function automatically detects and switches betw