Modern electronic equipment utilizes switching power supplies. These “switchers,” typically have distorted input currents which do not resemble the ideal, universally recognized, “sine wave” shape as shown in the top image on this slide. Average-responding AC ammeters (the least expensive and most common digital ammeters on the market) produce accurate readings only when measuring ideal sine-wave shaped waveforms. When average-responding ammeters measure distorted or irregularly shaped currents such as is shown in the lower image, reading errors can exceed 20% of their full scale input. When operated within its listed specifications, a true-RMS responding ammeter’s accuracy is not sensitive to the shape of the current waveform. True-RMS current measurements are very important in applications involving switching supplies and any other equipment which produces distorted waveforms, such as IT equipment and high end machines. Using an AC ammeter that provides accurate, true-RMS measurements, such as the ACM3P series, can significantly reduce inadvertent overloading of circuit breakers or fuses which can cause costly power outages.