Hello A&P Analog,
this device is use by an ear doctor to test the sensitivity of the ears.
If you hear in normal way a special headphone is connect to the output "AIR". The doctor can change the frequency and the level to see, when you can hear something. The frequency and the level is record on a sheet of paper in logarithmic scale.
If you are deaf, a bone shaker is connect to the output "Bone". This bone shaker is helt to your head to look if your acoustic nerve is funktion or not.
Regards
Rainer