Basic Report Design - Professional SQL Server 2005 Reporting Services - page 110

sum of product sales for the intersection of each of the groupings. By default, values are aggregated and
rolled up within groupings. To view detail values, use the plus sign (+) icon to drill down in one axis
(rows or columns) and then do the same for the other axis. Figure 4-54 shows a matrix report that has
been expanded to show details on both the axes.
Figure 4-54
The matrix control takes care of the grouping functionality in this report. As you can see in Figure 4-55,
the design is fairly simple.
Figure 4-55