When you create the fast formula BG_ABSENCE_DURATION (probably a copy from TEMPLATE_ABSENCE_DURATION), this formula is used to calculate the duration of the absences entered in your business group (BG). What's in a name.
Good to known is that this formula can have as extra parameters
- assignment_id (context)
- element_type_id (context)
- absence_attendance_type_id
The last one allows you to implement calculation rules per absence type.