Zoom
After loading, the image is automatically scaled to fit to window size. You can though change the image size using zoom commands.
Changing the zoom level
Rect Zooming 
, Zoom In, 
Zoom Out 
and Zoom Undo 
shortcut buttons are available on the toolbar.
| • | Rect Zooming - allows zooming using a rectangle selected on the image. |
| • | Zoom In (+) enlarges the image. This action can also be performed with the View -> Zoom In command. |
| • | Zoom Out (-) (or the View -> Zoom Out command) reduces the image. |
| • | Zoom Undo [Ctrl + U](or the View -> Zoom Undo command turns the image to the previous zoom size (if available). |
Also you can use "+" key for zoom in and "-" key for zoom out.
Zoom selection
You can select a rectangular area of the image by left-clicking on the starting point and dragging to the end-point of the rectangle. After releasing the button, the image will be zoomed so that the selected area is fit to the window size. Zoom can be canceled by pressing any key when the mouse button is pressed.
You can choose zoom value from zoom combo box 
in the toolbar, percentagewise to the original image size.
The Fit drawing to window 
button reduces or enlarges the image to fit the window. Double-click on the mouse wheel executes the same action.
Using the mouse wheel
You can use mouse wheel for changing the scale of the drawing. In this case, the mouse cursor points to the "central" point, around which the drawing will be scaled.