Martindale mm68 true rms trms digital multimeter martindale mm68 p martindale s mm68 is a true rms digital multimeter which measures ac voltage up to 750v dc voltage up to 1000v and both ac and dc current up to 10a it also measures frequency capacitance resistance and duty cycle and has a diode tester and an audible continuity tester which sounds when connected to a resistance of less than 100 omega p p the mm68 s 4 frac12 digit lcd screen displays measurement results as numeric v