Zoom into the picture. Left-click on a first point in the window. The mouse pointer will change its shape and show a rectangle {Sometimes this rectangle badly visible because of low-contrast}. Move the mouse to a second point and left-click again to select the rectangle for zooming in. Right-clicking will terminate the interactive zoom selection and switch to the textual mode, where you can enter the (world) coordinates of a center point x,y and a radius r for the zoom area. You can enter x = y = r = 0 to leave the zoomed view and return to the default. Note: The coordinate input mode is available by a hotkey: press z on the keyboard (while the graphics window is focused).