Here's a radio dial. Note
that it's marked in wavelength with the old style nomenclature
with LW meaning what it does today but medium waves were known
as "Short Waves".
A little later and descriptions became
standardized as Long, Medium and Short weavebands. About this
time international organisations attempted to fix broadcasting
standards and frequency allocations. After a couple of attempts
at convincing broadcasters to toe the line dials were able to
meaningfully show station names. Before this a list of stations
versus dial readings had to be kept. In fact some radio sets
included a chart fixed to the case on which could be pencilled
station names. See the Halcyon.
Before dials showed wavelengths they merely had a scale 0-180
degrees. Below is an echo of this where you can see a logging
scale marked 0-100.
This scale says it was made by "MONIX"
and has a provisional patent number 16523/31 presumably indicating
it was made in 1931.