from study, i suspect fringing capacitance effect on open transmission line or calibration kit will have effect on the accuracy of the KC901 VNA series measurement (including the latest KC901V). either the VNA designer has put default values for it or no at all in the calculation model, i dont know. but different open calibration standard kit will have different fringing capacitance effect, this will effect s-parm correction matrix if not input the right values, hence giving wrong measurement. i suggest KC901V designer will open up calibration kit data for user to enter in firmware, similar to brand name VNA like Keysight and Anritsu VNA. because i need to get 3rd party SMA Calibration Kit to move reference plane further away from KC901V for convenience measurement, most good cal kit will provide the data and parameters, but i cannot see it inputable in KC901V firmware, except just offset length. now, i cannot guarantee the KC901V will give me the right measurement, maybe just estimate.