Gridlines help define your plot area, making it easier to see the magnitude of your chart markers. To add gridlines to a chart, choose Chart, Chart Options, and then click the Gridlines tab of the Chart Options dialog box. Major gridlines connect to major tick marks, and minor gridlines connect to minor tick marks. You can change the position of both kinds of tick marks (and thus the number of gridlines that appear) in both of the following ways:
Select the axis whose gridlines you want to change, and then choose Format, Format Selected Axis.
Select a gridline from the set you want to change, and then choose Format, Format Selected Gridlines.
Either way, you come to a Scale tab that allows you to set the ...