How to fit in the range chosen by cursors on another graph?

Hello everybody!

Could you, please, advise me the best way to chose the cursors on one graph and then to use their positions for many other graphs to fit?

I'm trying to do it the following way: I call a function to display my reference wave:

function display_aver(CtrlName)  : ButtonControl
    String CtrlName
        string filename = "AvgTrace"
        Display $filename as "Average"
end

Then I would ask the user to set the cursors,
and then I'm trying to do my fitting on loop with pcsr(cursorName [, graphNameStr ])
But it does not work :(

    graphname="Average"
        FuncFit  doubleexpo W_coef   $filename[pcsr(A,graphname),pcsr(B,graphname)]     //fitting

I guess, the way I pass [, graphNameStr ] is wrong. How should I do it?

Thanks in advance!