Drawing a third variable curve on a 2 variable scatter plot in Spotfire

Question

I am trying to plot a curve (from Properties --> Lines and Curves) of Variable Z on a scatter plot of Variable X vs. Variable Y, in Spotfire. Is it possible to do this? I thought it would be "curve from data table" (Var X and Y are imported columns and Var Z is a calculated column) but it does not seem to be working.

Thanks]1