Let’s read in the data, which was created with CusterData-Create.nb:

iris=Import["http://ceadserv1.nku.edu/longa//classes/mat375/days/docs/Fletcher/data/Custar.csv","CSV"];
header=iris[[1]]
Custar=iris[[2;;]];
Custar[[1]]
Dimensions[Custar]

Now we’ll split up that matrix Custar into splitData, and then we’ll start peeling off certain variables, e.g. maxes:

splitData=Transpose[Custar];
maxes=splitData[[3]];
mins=splitData[[6]];
ListPlot[maxes,PlotLabel->header[[3]]];

dtr=maxes-mins;
xs=Table[i,{i,0,Length[dtr]-1}];
xs=xs/365.25;

data=Transpose[{xs,dtr}];
dtrlm=LinearModelFit[Cases[data,{_?NumericQ..}],{x},x]