You can show gridlines to make the values in a chart easier to read. (For more information, see Showing/hiding gridlines.)
Gridlines are a network of lines that extend across the plot area, starting from one of the axes of the chart.
The following types of gridlines are available:
▪Major gridlines are indicated at every major tick mark on the axis.
▪Minor gridlines subdivide the major grid into an even finer grid if necessary.
Changing properties: To change the properties of the major grid of the value axis, for example, select one of its gridlines, right-click on it and choose the command Value axis major gridlines: Properties from the context menu.
Tip: Alternatively, you can chose this command via the Edit properties icon 
on the ribbon tab Chart.
You can make the following settings:
Format tab
Tip: The appearance of the lines can also be conveniently adjusted directly via the buttons of the ribbon tab Chart | group Chart elements. For more information, see Editing chart elements.
▪Line section
| Here, you can change the line style used to draw the gridlines. Auto uses thin gray standard lines. None removes the lines. The option Custom lets you customize the line style. |
Changing the scale of gridlines
To change the distances between the gridlines, select the corresponding axis, choose its properties and make the desired changes on the Scale tab.