About calculated data
Most business reports require calculations to track sales, finances, inventory, and other critical business activities. You can keep a count of items in a warehouse, or provide more complex financial data, such as tracking stock portfolio performance over time. Some of this calculated data can be included in the data set if the person who created the data set knew that you and other users need to work with this type of data.
Sometimes, however, a data set does not provide all the data you want to display in your report. In this case, you can create your own calculations. To do so, you create a new field called a computed column. Figure 3-1 shows a report design that uses a computed column, Total, to display the total of each order line item. In this example, the Total values need to be calculated, because the data set does not include this data.
Figure 3-1  

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