When
drawing, the edges of the main view have an area that act as an auto-scroll area
– if you move your mouse in that area while drawing your page will scroll
automatically which gives you more room to continue drawing. Sometimes this is
undesirable, and the action can be toggled on and off using this button. Note
you can also use the arrow keys while drawing to scroll 1cm per key click. And
holding the spacebar will let you pan the screen by dragging it with the
mouse.