There are a number of Fields that can not be REMOVED from the List of Fields. I understand this for ITEM-specific fields and other System-related fields. But fields like "ThisWeek" and "AddressBook" don't fall into those categories. I know that a number of these fields are referenced in Equations and the default VB Code but other similar fields like "Duration" are not Locked. Is there specific criteria for Fields that can't be removed Databases?