The Zoom Out on the canvas icon allows the user to shrink the contents of the canvas by a factor of 5%. In other words, if the zoom factor would be 100% and this icon is selected then the zoom factor would be 105%.
How to zoom out on the canvas
Click on the Zoom Out icon. The viewing factor will be increased by 1% each time you click on the icon. The viewing factor is reflected in the Zoom Canvas Box.