Grids
You can divide the axes into sections by assigning gridlines to them. This allows you to get a better overview of the chart, especially if you are working with large charts. The Y axis major grid is activated by default.
Main grid
Defines the axis to be set as the main grid.
X axis
Adds gridlines to the X axis of the chart.
The Vertical Grids icon on the Formatting bar toggles the visibility of the grid display for the X axis. It switches between the three states: no grid, major grid and both major and minor grids displayed. The change will affect check boxes in Insert - Grids.
Y axis
Adds gridlines to the Y axis of the chart.
The Horizontal Grids icon on the Formatting bar toggles the visibility of the grid display for the Y axis. It switches between the three states: no grid, major grid and both major and minor grids displayed. The change will affect check boxes in Insert - Grids.
Z axis
Adds gridlines to the Z axis of the chart. This option is only available if you're working with 3D charts.
Minor grid
Use this area to assign a minor grid for each axis. Assigning minor grids to the axis reduces the distance between the main grids.
X axis
Adds gridlines that subdivide the X axis into smaller sections.
Y axis
Adds gridlines that subdivide the Y axis into smaller sections.
Z axis
Adds gridlines that subdivide the Z axis into smaller sections. This option is only available if you're working with 3D charts.