The Toggle
Ruler icon allows you to turn on or off the ruler located on the
top and left sides of the grid. The ruler shows the size of the grid in
inches or centimeters. It also displays your cursor's position along the
grid's horizontal axis (top ruler) and vertical axis (side ruler). You
can switch between Inches or Centimeters by right-clicking on the ruler
and selecting the desired option from the shortcut menu.