Click on the 1:1 to zoom in on the pages.
Click on the magnify glass to zoom out of the pages.
 

This version will give a viewer a high resolution format for PC, Mac, Ipad and other similar tablet devices.

On PC "Ctrl & +" or "Ctrl & -" will zoom in and out on your browser.
On Mac "Cmd & +" or Cmd & -" will zoom in or out on your browser.