Select Options® Grid density.
This option allows you to determine how densely vertical grid lines should appear in the plan. Choose Coarse if you want fewer lines and Fine if you want more. The figure under Displaying a Horizontal Grid shows a Coarse density.
For example, if the current time unit is Days, Coarse grid lines appear at every month-boundary, and Fine at every week-boundary.
This option has no effect if the Vertical grid option is not turned on.