Set ruler preferences
You can set the ruler to use different increments (points, inches, centimeters), or show the tick marks as percentages. You can also place zero at the center of the ruler.
Set the ruler increment
When you set a unit preference for rulers, it applies to all presentations. You can change the preference at any time, even if you have a presentation open.
If you don’t see the ruler, click in the toolbar, then choose Show Ruler.