Back around 1998/1999 at the old ham club, we pooled an bought a gadget that you could plug in (like a shunt, with fancy electronics) that would give you detailed information about whatever you were powering, including start-up cycles, all the majikal trig stuff, and average power consumption over time, etc...
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I bought the device detailed in the link below. I was astounded at the specs: real power, apparent power, power factor, and other stuff. The accuracy is stated as around 1%. The device is $30 at home depot. This would be a good investment for anyone trying to size an inverter, generator, or other power source. One can understand the loads of their furnace, refrigerator, or other device.
I have an older version of that. Had to replace a fuse inside after attempting to check out my microwave.