In general terms.
Can we say that the variance
of an inductance containing a variometer
is zero to twice the inductance of the rotatable?
The variometer is not talked about much these days
so it is difficult to determine if something
else is at play other than what apears obvious.
I use such a set up in a coupling situation
together with variable physical separation to
prevent kickback and interference from tail
end unused inductance
I am not knoweledgeable enough to understand
all the possible implications so the variometer
seems the best place to start
Regards
Art