You also want to use 'C' weighting, and SLOW response on your meter.

I saw the specs on this meter, quite a nice unit.

It is also recommended that you put the meter on a tripod, facing up, not directly at a speaker. Set it up at your sweet spot, and read the meter from a few feet away to keep your body from interfering with your readings. Keep the 990 remote in your hands, and have fun!

Could you first run the calibration with the 990 mic, then compare the results with your meter? I'm curious just how accurate the 990 auto cal is.