Potentiometer Range in Speaker Frequency Response Curves
This is from a format used by Bruel &amp; Kjaer in their level strip chart recorders. The "potentiometer range" parameter indicates which scale to use for the Y axis. In the case for the CUI device the range is 50 dB so the left scale on the Y axis is used, and the 25-dB scale on the right is ignored. The "zero level" parameter is 60 dB so the bottom of the Y axis is 60 dB and the top is 60+50=110 dB. Since it's a speaker output test dBSPL is implied for Sound Pressure Level (SPL). The 1-kHz level on the plot is just a bit under 89 dBSPL, and this correlates well with their "sound pressure level" specification of 86 to 92 dBSPL (average of 4 frequencies).

This system dates back to the 1970s and I would guess that nobody actually uses one to perform measurements, but has the output from a "modern" system format the results to look like the output from the strip chart recorder.

The potentiometer was a box installed in the recorder that determined what the Y axis would measure: linear or log (dB) and what range. Different potentiometers would provide different results and require the user to install the proper chart paper (linear, dB, range).

As the pen moved back and forth on the paper (which was up and down the Y axis), a wiper mechanically linked  to it would travel across a linear contact element on the potentiometer, which had an internal network to provide the proper range and taper. Here is picture of the B&amp;K 2307, and the potentiometer module is the big square box to the left of the chart roll:
B&amp;K 2307