This degenerated, but I do like the ability to estimate with body parts. 300 mm does nothing for me mentally. 30.0 cm does a better job.

The TS/OP can 3D print a part. Also look for ones that have already been done.

....
Good thing there was no problem with changing from " cps, kcps & Mcps "
to " Hz, kHz and MHz ".

Or was there .....

There was, sort of, I had a valve car Blaupunkt radio whose dial was graduated in increasing wavelength (Not frequency). That's the a RPN (reverse Polish Notation) radio vs an Algebraic radio that everyone uses.