I thought his articles were all pretty complete.
He had an electrically powered "shaker" on the instrument panel to overcome the internal friction of the altimeter and he had a stopwatch. He flew set airspeeds and recorded the vario readings and altimeter readings while flying.
He did most of his testing in the winter on calm days when the airmass would be most stable.
I think he also had a calibrated airspeed indicator that was connected to a "bomb" that was hung out the window to compute the airspeed/pitot error.