The Counter option causes the counter number for a particular field to be increased by 1 every time that this field is found within the data set currently being read. The resulting counter total is displayed in much the same manner as a grand total at the end of the basic list. Just as with sum totals, counter subtotals can be displayed for individual control levels. These counter subtotals show how many values have been assigned to a particular control level.
Unlike totaling, counting fields are not displayed automatically. Fields you want to display counting fields for must be dragged to the Counter toolbar. This toolbar can be displayed by choosing Tools ® Counting fields on/off.
The Counter option can also be selected for non-numerical fields.
Example
In this example, suppose you want to generate a list which contains booking information for each flight. A subtotal of revenues per booking should be displayed for each flight and a line containing a sum total of everything should appear at the end of the list. In addition, you want to know how many bookings were made per flight.