Autodesk 24108-051400-9000 - AutoCAD Revit Architecture Suite 2008 User Manual page 863

NOTE As you move the grip, the original base height value is displayed in addition to the new base height and
the difference between the two values.
After selecting the grip, you can also enter a new value for the base height of the curtain wall.
Changing the Length of a Curtain Wall
Use this procedure to change the length of a curtain wall with grips.
1 Select the curtain wall.
2 Select the Lengthen grip, move the grip until the length value you want is displayed, and click once.
Using Grips to Edit Curtain Walls | 823