On Thursday, July 9, 2015 at 9:29:58 AM UTC-7, Jim Wilkins wrote:

[about odd AC measurements on a DC/AC inverter]

If you have a (possibly sacrificial) way to heat water with the
inverter you could time how long a measured amount of room temperature
water takes to boil on the inverter and on Netzstrom. They should be
pretty close to each other.

Bingo! An electric coffeemaker's brew time for a given water fill is
a better RMS voltage meter than most inexpensive electronic meters.