Variogram in Universal Kriging

[patagoniasf]

Hi! First of all thanks for the package, it is really helpful.
I'm new to kriging and I'm trying to understand some things.

As I understand, Universal Kriging uses the residuals variogram to solve the kriging equations. The variogram fitted (and returned) when creating a pykrige.uk.UniversalKriging instance is the residuals variogram then? If I pass a custom variogram, should I pass the residuals one?

Thanks in advance.