[BC] Article in RW Workbench--Question?

[Dave Riddle]

Recorded on a "correct speed" reference recorder.
>
> I fail to understand how this would work, because if the tape speed is
the same for both the recording and the playback, comparing the tone
frequency of the audio oscillator and the tape playback will show no
difference, irregardless of what the tape speed actually is, whether it's
correct, or fast, or slow.
>