Ananth, you haven't been lazy at all. You paid good money for the 3805 and its microphone and you're justified in relying on the results that it gave you. There's no sound reason(intended)to assume that a manual calibration will be more accurate(or even as accurate)than what the 3805 has done. Since you indicate that you already have an RS meter, it'll be interesting to use it to doublecheck the center channel level compared to the mains.

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Enjoy the music, not the equipment.