newbie help with Speaker Workshop

Hi all

I've quietly been playing with speaker workshop recently but Im having issues.

I do the setup and calibration as described on the guides I have found but...

When I test passive components I get "close" to the actual values but with repeat testing it always varies up and down.
When I test drives I get messy charts that just dont look like I think they "should".

I suspect its my cheap soundcard or the little external amp I'm using.

How accurate should my results be for testing my reference resistors ?

Regards