I would like to ask for help. I intent to fit two different datasets y1-x1 and y2-x2 with two fitting functions y1=f(x1) and y2=f(x2) which contain the same set of parameters. When I try to fit them, NLFit dialog will visualize four plots y1=f(x1), y1=f(x2), y2=f(x1) and y2=f(x2). But I want to fit only y1=f(x1) and y2=f(x2) dependencies, because y1=f(x2), y2=f(x1) are meaningless for me. I am using Origin 9.0 Many thanks for your help in advance Ivan