help with Magnetic Flux Gradient in mf module

Hi all,

I have a problem with the magnetic flux gradient calculation in a quadrupole solved with the mf module.

If I simulate permanent magnet quadrupole I use the mfnc module and if I want to know the B gradient I define a cutline in the middle of the quadrupole equal to the bore diameter on the x (or y) axis
Then I select a line graph with that line as source and I plot d(mfnc.By,x) (or d(mfnc.Bx,y). The result is the field gradient of the quadrupole

If I do the same with a EM quad I have a gradient equal to zero even if the mf.By plot is not constant (it is correct as it has the tipical quadrupolare shape).

How I should calculate the gradient?

Thanks
Francesco