This object has 4 halved discs and 3 solid discs ...
With the shape of an ellipse, the variable capacity that is related to the angle of rotation is linearized!
It is the air that serves as insulator for this condenser!
When the half discs are 100% opposite: you get the maximum capacity!
And minimal when the opposite but check!
At least: 11.5 pF
Capacity increases when overlap increases ...
For a maximum of 57 pF, a ratio of 1 to almost 4!
We can not reach 0 because the centers of the discs remain opposite!
What is the origin of this component?
This variable capacitor used to select the frequency of the tuner (radio station TSF at the beginning of the twentieth century!)
The tuning was related to the selected resonant capacity with a coil! Regular tuning was required! Air humid ...