You can enter values in the Null Values, Distinct Values and Average Length fields.
Alternatively, you can automatically populate them during reverse engineering by selecting the Statistics check box in the Reverse Engineering dialog box (see Reverse Engineering from a Live Database).
You can refresh the value of these fields (along with those for all of the table's columns) at any time by right-clicking the table symbol or its entry in the Browser and selecting Update Statistics from the contextual menu. You can also update the statistics for all tables by selecting (see Reverse Engineering Database Statistics).