Have you added a callback to your graph button? Because it is within this callback that you will want to read the data from the Excel file (see xlsread) and then plot columns 2-4. An example could be
function btnGraph_Callback(hObject, eventdata, handles)
% hObject handle to btnChangeMarkupColour (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% read the data from the Excel file
data = xlsread('excelFileData.xlsx');
% get the handle to the axes/plot from the handles object
ha = handles.axes1; % example only, the name for your axes may be different
% set the current axes
axes(ha);
% plot the data (use hold on for multiple plots on same set of axes)
hold on;
plot(data(:,2),'b');
plot(data(:,3),'r');
plot(data(:,4),'g');
You will need to write some additional code to determine the steady state(s) for each set of temperature data.
