The command sets an axis for subgraphs. As global axes, these axes are used only for information about the ranges of the axes. They do not define the places of any objects. In addition, several operations, such as bars, skips over this definition and they locate objects in the default range [0,1]. If the parameter <index> has been given, then the axis definition is due to this subgraph. Otherwise the definition is set over all the subgraphs. See an example from Sect. 7.4.2.