I connected my Boonton power meter calbrator output to my DSOX3024 with a 50 ohm load into ch1 (power meter calibration is due next month). When I select the AC, RMS, FS measurement it reads 228 mv. The output of the calibrator is 50MHz, 0dbm (1mv) into a 50 ohm load. I don't understand why the 3024 measuring 228 mv when the signal is only 1 mv. The signal is a pure sinewave.

P=V^2/R ->

V = sqrt(P*R) = sqrt(0.001 W * 50 Ohm ) = 223 mV

spot on