De acordo com os morados da Adobe :
Rulers help you accurately place and measure objects in the illustration window. Rulers appear at the top and left sides of the illustration window. The point where 0 appears on each ruler is called the ruler origin. The default ruler origin is located at the lower-left corner of the artboard.
No entanto,
To change the ruler origin, move the pointer to the upper-left corner of the illustration window where the rulers intersect, and drag the pointer to where you want the new ruler origin. As you drag, a cross hair in the window and in the rulers indicates the changing ruler origin.
Mas:
To restore the default ruler origin, double-click the upper-left corner of the illustration window where the rulers intersect.