Tablet Master-Detail View is Split in Half


The picture on p. 369 shows master-detail screenshot with list on left and detail on right.
The list on the left takes about 1/4 of width.

On my emulator (Nexus 10), the list takes 1/2 of the width. And I can not drag the divider to resize this.

How can I set the width of list to take less screen or how to make divider draggable so I can manually resize?
Much appreciated