Art Unwin, KB9MZ wrote:
"The markings are 3600 - 5000 KC."

"KC" may date the variometer back several decades or more.

Inductance has units of flux linkages per amp.

A single-layer solenoid has an inductance in microhenries of:
L = (n squared) (d) (form factor)
n = number of turns
d = diameter of the coil
form factor = complicated constant that depends on the length to
diameter ratio

See Terman`s 1955 edition, page 11 for the inductance story.

Inductance does not have a frequency term in its formula, but inductive
reactance is proportional to frrequency.

I guess that the variometer`s frequency markings are related to Q.
Resistance rises as the sq rt of frequency due to skin effect. Q will be
inversely proportional to r-f resistance in a coil.

As Reg Edwards has already said, a variometer`s Q is likely very poor
when set for low inductance. Q is XL/R.

Changing the variometer`s inductance setting has almost no effect on its
resistance. Its Q will be low enough at maximum inductance setting on a
shortwave variometer. Lower XL and don`t change the R. The effect on Q
is obvious.

I suspect the variometer was optimized for Q in the 3600 - 5000 MHz
range.

Best regards, Richard Harrison, KB5WZI