Chad -- what are you measuring FOR? If it's balance b/ween the spkrs, then you have an IMbalance in the mid-bass and lower between L-R. This is probably due to spkr positioning/room interaction.
So, for the ratshack you get a chart which shows you how far off from reality the meter is at each frequency -- and you compensate to get the real -life reading.
I never really understood what people mean when they say it needs to be re-calibrated.If you measure sound pressure against a "reference" -- say 1kHz -- you want the measuring device to equally sensitive at all other frequencies. If it's not, then you'll get a lower/higher reading at some frequencies even the the actual sound pressure level may be the same.... it;s just that the meter isn't reading correctly.
So, for the ratshack you get a chart which shows you how far off from reality the meter is at each frequency -- and you compensate to get the real -life reading.