These Fluke DMMs 15, 17, 18 (also 101, 106, 107) are not able to measure true-RMS! Considering the price, they are not worth to buy! Even Fluke says on their HP: "Yet a true-RMS meter is widely preferred because it is the only one that can accurately measure both sinusoidal and non-sinusoidal ac waveforms." More @Wikipedia
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