This variometer (variable inductor) was purchased in a radio trash an treasure event here in Canberra a few months ago. I don't know anything about it, and have no idea if this was used in a low power transmitter or a receiver to tune the antenna to the lower frequencies.
Its inductance can be tuned by selecting the closest position on the 12 position switch (see below) and then rotate the spherical shaped inductor inside the coil by using the know (below as well).
The inductance can be varied from about 140 uH to 12.5 mH.
