Brilliant!
The BBC Audio Test Set EP14/1 in all variants has a similar arrangement for the frequency set control. A (flywheel-equipped) spindle has a rubber grommet that presses against the surface of an aluminium disc connected to the Wien Bridge oscillator's air-spaced capacitor. It serves as a 'mitre box' * and reduction gear combined.
Guy
* (any bus enthusiasts out there will know this is a 'Bristol VRT transmission' term
)