The widely used method for adjusting tape azimuth uses a stereo tape and an
oscilloscope, and adjusting the azimuth to make the 2 channels in phase.

That's fine, I'm sure, for a calibration tape, but to adjust to a
pre-recorded tape it is less than ideal because if the tape was already
recorded with an az error, this method will restore the correct phase at
the cost of a rolled-off high-end. I'd rather have the high-end.