Calculations are functions that return a value. A calculation cannot actually do or update anything itself; all it can do is return a value. Where the calculation is defined, determines what that value is used for, or what the value causes.

The value returned by derivation calculations, sets the value of the attribute the derivation is attached to.

The value returned by validation calculations, determines whether the value of the attribute is valid or not. (If true, ie not zero and not null is returned, the value of the attribute is valid; if false, ie zero or null is returned, the value of the attribute is invalid. If any attributes fail validation, the instance will not be written to file, regardless of how many other attributes passed validation.)

Error message calculations return the text to be used as the error message, should the attribute the error message calculation is attached to fail validation.

Calculations can also be used on templates, in order to derive and display specific values on the page being returned, and in order to determine if parts of the page should be returned or not.