Microsoft Project enters certain data into special fields called calculated fields. For example, when you enter a task duration, Microsoft Project automatically performs a calculation to determine the task’s start and finish dates. It enters the calculated dates into your Start and Finish fields without your having to do so manually. Actually, this is one of many such calculations Microsoft Project performs automatically. So don’t be surprised next time you see data that you didn’t enter.
That completes the flow of data: from you to the Microsoft Project interface, "down" to the database, back "up" to the views, and then finally out to you once more. In this flow you and Microsoft Project are interdependent partners. Microsoft Project depends on you for complete and accurate information. And you depend on Microsoft Project to create an accurate schedule from the information you enter.