We describe estimation of the magnitude and phase response of a sampling oscilloscope with 50 GHz bandwidth using the nose-to-nose method. The measurements are corrected for the non-ideal properties of the oscilloscope and calibration apparatus, including mismatch and time-base distortion, drift, and jitter. The mean and standard deviation of repeated measurements of an ensemble of three oscilloscope samplers are reported, along with attempts to verify the magnitude calibration using a swept sine-wave method.