While NBC maintained a strict policy of “No Recordings” throughout the 1930s and ’40s, the recording room still saw lots of activity. Some programs originating in New York or Chicago were recorded here to “time shift” them to a more appropriate hour for the West Coast. The recording restriction also did not apply to programs broadcast only on the local stations, KGO and KPO.
In this view, the engineer is inspecting the cutting depth by viewing the recorded grooves through a microscope. The microscope contained a graticule which allowed direct measurement of the cut depth by measuring groove width. The vacuum hose at the center of the turntable was used to extract the acetate shavings removed from the disk in the recording process.