The argument of the method Draw("AP") is important here. Behind the scenes,it tells the TGraphPainter class to show the axes and to plot markers at thex and y positions of the specified data points. Note that this simpleexample relies on the default settings of ROOT, concerning the size ofthe canvas holding the plot, the marker type and the line colors andthickness used and so on. In a well-written, complete example, all thiswould need to be specified explicitly in order to obtain nice and wellreadable results. A full chapter on graphs will explain manymore of the features of the class TGraphErrors and its relation toother ROOT classes in much more detail.