During the implementation stage of product development, some companies divide implementation activities into two categories: Day 1 functionality and Day 2 functionality. In the context of product implementation, Day 2 functionality refers to administrative and systems processes that must be in place and functioning before a product can be introduced to market mathematical models that test the relationships among assumed values for variables such as expenses, interest rates, and persistency systems and processes that are necessary at some future date to service and administer a product, but which can be implemented after the product has been launched a review of a product's early sales performance to identify potential weaknesses and make necessary changes in distribution or promotion