Fluke 381 review in Lighting Posted August 23, 2021 On 6/20/2015 at 8:06 AM, Guy Holt said: Since the advent of electronic HMI ballasts, measuring hertz is not as important as it was when HMI ballasts used magnetic ballasts. In those days you had to make sure the generator was spinning so that the frequency was +/- a quarter cycle of 60Hz (59.75-60.25Hz) to avoid flicker. By squaring off the waveform to the globe, electronic ballasts eliminate flicker except at very high speeds in which case you need to use 1000Hz high-speed ballasts. If you will be using electronic HMI ballasts, you want to make sure you get a meter that reads true RMS. In an introductory workshop my local, IATSE Local 481, offers for set electrics we do an exercise where the students meter the voltage and current on a putt-putt generator (non-inverter type) while running a non-pfc 2.5kW HMI light. Since, invariably, the meters brought by the students range in quality, the readings they get range from being 84% over to 40% under what they should be. We then so the same exercise with tungsten lights and they all read the same. The discrepancy in the results is a good jumping off point for a discussion about how meters work and that they can be mislead by the distorted waveforms drawn by some electronic HMI and Kino ballasts. Since the consequences of under measurement can be significant - overloaded cables may go undetected, bus-bars and cables may overheat, fuses and circuit breakers will trip unexpectedly - it is important to understand how meters work and why only meters based on "true RMS " techniques should be used on power distribution systems supplying nonlinear loads. To see why that is the case use this link: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorMeters Guy Holt ScreenLight & Grip Lighting Rentals & Sales in Boston What particular True RMS meter would you recommend, Guy?