NumberDropDownField.Index — Number
Returns the position of the selected item in the number drop-down field, starting with 1, or a blank value if no item has been selected. If the first item is selected, 1 is returned, if the second item is selected, 2 is returned, etc.
The Size property returns the number of items in a number drop-down field.
This property is a read-only property, meaning that no formula can be assigned to it.