You can do this, but it's pretty advanced. The basic idea is to copy the values into an array as the crosstab is being generated. Then you can subtract one column from the other column by using the array index to identify which items to substract. To print the difference in another column, you can use a formula in the Text property of the cross-tab cell. This overrides the current value with your calculation.
I wrote about this in my Encyclopedia book and give a full working example of how to do it (takes quite a few pages as you can imagine). If you think you want to do this, I suggest checking out my book for the full tutorial and instructions. It's in the last part of Chapter 13. You can find out more about my books at
Amazon.com or reading the
Crystal Reports eBooks online.
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