Vulnerability curves are generated to measure how hydraulic conductivity declines at increasing levels of drought and xylem tension (http://biologylabs.utah.edu/sperry/methods.html#vulnerability_curves). The centrifuge method has been developed in John Sperry's laboratory at the University of Utah. It has been successfully modified by Li et al. (2008). We recently confirmed once again that centrifuge curves (using the classic rotor design) accurately reflect the loss in conductivity, i.e. they agree with native embolism/water potential measurements.
Curves have been measured for different species and plant organs. Root xylem tends to be more vulnerable than stem xylem, consistent with roots having less negative water potentials.