Stress-strain graph

Hi everyone, I am studying an example in Abaqus example problems manual (version 6.10) called "uniaxial rachetting under tension and compression". In the example there is a graph plotting axial stress-strain relationship for experiment data and simulation data. By studying the inp file I knows that the writer has ask for some outputs like RF1, RF2, RF3, S, ALPHA, ALPHAN, LE and so on in certain node and element set. However, I still can't figure out how writer use the output data from simulation to plot the axial stress-strain graph.