Summary (crosstab) reports are a special kind of report. They summarize records of various types in a grid format. You define the columns and rows along with the values to be summarized, then VSys totals the values.
Summary/crosstab reports are exported to Excel rather than printed. This affords you much more flexibility in how you present the data rather than being restricted to how VSys would do it automatically.
You'll regularly use calculated fields here to distill the information down. Rather than using the date of an assignment, for example, you're more likely to want the month, quarter or year in order to have columns and rows that make sense.
Use the five built-in sample reports: Account Records by Quarter, Active Status Transitions Summary, Person Type Transitions Summary, Survey Summaries and Volunteer Counts by Active Status and Date Started as examples on how these reports work and what you can get from them.
