IBM 3270 Manual page 109

Changing the Size of the Second Window
Let's place your second window in the upper
right corner of the screen. First we will change
its size:
1. Press the Jump key.
Your second window will appear and cover
the entire screen. The line at the bottom of
your screen changes to:
WSCTRL SETUP MOVE WINDOW=D SCREEN=O
Window D is shown.
9-12 Book 3 - Using the Control Program