As you’ve seen in the past three chapters, FileMaker’s calculation functions can do everything from text processing to financial analysis. Since calculations show up in so many different places in FileMaker, you might want to use the same calculation more than once. It would be a shame to have to type it in every time—and then make changes in several places the next time you need to modify it. In fact, a creative person like you may need a unique calculation to do something FileMaker, Inc. never thought of.

For these situations and more, FileMaker provides two ways to extend the calculation system. The first, called Custom Functions, lets you design your own calculation functions using the same syntax you use to create a calculation. You can then use these functions in any calculation in the same FileMaker file.