To define a part of the graph as the graphing zone (« Zoom Box »), put the mouse into the graphic tab and then keeping the « ctrl » key pressed, draw a rectangle with the mouse while pressing the left button. After releasing the button, you will be asked for a confirmation.

Figure 52 : Confirmation de zoom

After clicking Yes, the rectangle will cover all the graphic tab.

Figure 53 : Zoom

Moving the mouse while pressing the left button, without pressing the « ctrl » key will move the graph inside  the graphic tab.