Hi, jethro holcroft, I didn't have much time to go much into your problem but I am very confused as to what you do, I've done the following but I still do not understand much, would serve too that put a step by step what to do so I can help you more, I agree with you that I have advanced
In[1]:= prb = Import["C:\\Users\\luis\\RegressionExample.xls"];
In[2]:= corr = Rest[Flatten[prb, 1]];
In[3]:= tif = Fit[corr, {1, x, y}, {y, x}];
In[4]:= xmax = Max[corr[[;; , 1]]]
Out[4]= 2271.86
I hope to have helped you although it is a little
