I used to calibrate,& sometimes, fix these sort of devices.
I vaguely remember that particular model.
Although most of the newer stuff was controlled from a laptop, there was still a lot of older standalone gear around.
The audiometer headphones must deliver a precise sound pressure to the ear of the person under test.
To this end, Audiometers (complete with headphones) are calibrated using an artificial ear, which is in turn calibrated in an Acoustic Standards lab.
In the local calibration, each of the headphone earpieces are placed on the artificial ear, & a series of tests are carried out, including absolute output capability, frequency response, noise & distortion.
A calibration chart is drawn up for both channels.
They are rather nice pieces of equipment, but whether they are worth keeping for historical interest is
anyone's guess.
It might be worth contacting the manufacturer to see if they have a Museum,which may need an example of that model.
Otherwise, I'd probably pull it apart for the useful bits.