button next to a member’s name indicates that that level can be drilled down.Drilling down lets you view a detailed breakdown of the data by expanding the lower levels of the grid members. A plus button next to a member’s name indicates that that level can be drilled down.
Drilling up lets you hide lower levels of data by collapsing the grid members into higher levels. A minus 
button next to a member’s name indicates that that level can be drilled up.
When you drill up or down in the grid, the chart automatically focuses on the drilled data.
To drill down a member:
Double-click on the member heading or click . The member expands showing its child members. The plus button changes to a minus button.
In the example below, the Accessories and Bikes members (Category level) have been drilled down to display the next level (Subcategory level).
To drill up a member:
Hold down Shift and double-click on the member heading, or just click to contract the display and view only the parent member. The minus button changes to a plus button.