1. Choose from a variety of items in the [ZOOM] menu.
[ZOOM] "6:ZStandard" is a common choice. From there you can zoom in or out.
2. Use [ZOOM] "1: ZBox" to zoom to a particular part of the graph.
Go to: [ZOOM] "1: ZBox". Use the arrow keys to position in the upper left corner of what you want. [ENTER]. Use the arrow keys to go down and to the right to form a box. [ENTER].