a dummy sine generator :
Op Amp version :
the x = Δf( L( f ) ) = – 2 · Δf / ( (2π) ² · C · f ³ )
where Δf = f(40uH) - f(42uH)
the y = ΔL( f ) = L(42µH) – L(40µH)
and the best match for the ΔL is a non-std. average E( x , y ) = 2 · x · y / ( x + y )
[Eop]