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.
Choose Keynote > Preferences (from the Keynote menu at the top of your screen), then click Rulers.
Click the Units pop-up menu, then choose an increment.
To show the ruler marks as a percentage of the slide, select the “Display the ruler units as percentage” checkbox.
Place zero at the center of the slide
You can place zero at the center of the ruler and show ruler units increase to the left and right.
Choose Keynote > Preferences (from the Keynote menu at the top of your screen), click Rulers, then select the “Place origin at center of ruler” checkbox.