it seems that this post it's talking about the same thing ... "calculate dV/dI where I and are 2 vectors results of measurement" (http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=506500000008000000112A0000&UCATEGORY_0=_49_%24_6_&UCATEGORY_S=0)
good luck
