You can change the data series whose values are used to calculate tick-mark labels along the x axis in an xy (scatter) chart. By default, the values in the first series on the datasheet are used for tick-mark labels. An "X" appears in the row or column heading next to the data series you have assigned to be plotted on the x axis.
Switch to the datasheet.
Click the row heading or column heading of the row or column you want to use as the values along the x axis.
On the Data menu, click Plot on X Axis.