If you have not already done so, insert a Line chart by selecting it from the Insert menu, or double-click an existing chart to access the chart's configuration panel.
Access the Chart tab.
If necessary, in the Appearance section, select Line Chart from the list box. The Layout section appears.
If you want to set the margin of the plot area to be half the interval between data points, select the Use Default Margin check box.
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To specify the amount of space for the plot margin (the amount of space between the first and last data points and the left/right edge of the plot area) make sure the Use Default Margin check box is not selected, and select the number of pixels from the Line Plot Margin list.