The calculation of the key decision factors may require complex business recalculation, which may be served by custom "calculator" rule classes.
Typically the implementation of keyDataTimelines will reuse calculation rules which you have already implemented for eligibility/entitlement calculations, although on rare occasions some refactoring of the existing rules may be required to make the common rules suitable for both eligibility/entitlement and key decision factor purposes.
The calculations will typically ultimately retrieve (and thus depend on) entity, evidence or rate data. These dependencies behave in a similar way to those for eligibility/entitlement calculations (see E) Custom rule classes for calculations).