Hi Leon,
it depends on how accurately you know the properties of your cal elements.
Do you still have the kit parameters of the manufacturer?
If so, do the standards still obey these parameters, i.e. not worn, clean?
Cables are another issue. Are your test cables stable when you move them, i.e. amplitude stability, phase stability?
As far as I have found out, the 8510C assumes the load standard to be ideal. Thus, the return loss of your load will limit accuracy of measured reflection coefficients near the 50 Ohms point, while short and open will impact high reflection coefficients.
Transmission is yet another story.
Sorry, no simple answers possible.
Best regards,
Tom
