Joe, you also shouldn't overlook the possibility that using the SPL meter(the RS model isn't extremely precise and claims +/- 2dB accuracy)and adding in human error in using it may result in the auto-calibration done by the 2400 being at least as accurate. If there are differences between the two it shouldn't be assumed which is more nearly correct, as we sometimes read(i.e. using the meter to see how far the auto-cal is "off").

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Enjoy the music, not the equipment.