How to Set X-Axis Position
The X-Axis is positioned along the bottom of a graph by default, but you can move the X-Axis to be at the top of the graph, or at a specific vertical position on the Y-Axis scale.
via Inspector
In the Inspector's "Graph" pane under "X-Axis", use the "Axis Position" buttons. If you set the X-Axis Position to "bottom" or "top", you can also specify an offset from the edge of the graph (ie to provide a margin between the x-axis and the graph plot). If you set the X-Axis Position to Y Intercept, you can place the X-Axis vertically at a numeric value according to the Y-Axis scale.
