Hi Chris,
1)Right click in the Chart Area (the white border on the chart)
2)Select he Source Data item from the popup menu
3)Open the Series tab
4)Note the item X-value ....Sheet1$A$10...<red thing>
Click the red thing, select the read x-values with mouse, click the red
thing again
OR carefully type the correct cell references for the x-values
5) Repeat step 4 for y-values.
Note you can do the same thing while making the chart: follow instructions 3
and 4 at Step 2 of Chart Wizard
Best wishes
Bernard