During Powers's cab ride away from Walker's apartment, the Chicago Theater is visible in the rear-projection behind the car. After several more minutes of driving, the cab turns around in front of the same theater.
The recording machine that creates a major plot point is a Wilcox-Gay disc cutter that could record at 78 or 33 rpm on a maximum disk size of ten inches. It cut at a fixed 96 lines per inch. Unfortunatly those specs limited recording time to about 3 minutes at 78 rpm and only a bit more at 33. A real professional would have used something like a Presto which cut 12 inch discs or a broadcasting machine like a Scully that could cut 16 inch disks. Even the FBI used disk cutters in pairs so one could begin recording when the others had used up all its blank disk surface. A much more likely device would have been a wire recorder which despite its limited fidelity could record speech for an hour. These units were not cheap but Dr. Ritter was obviously wealthy. Her Wilcox-Gay recorder had a retail price at that time of about $100.00 and was among the lowest priced recorders sold.