To change the rulers’ zero origin, position the pointer over the intersection of the rulers in the upper-left corner of the window, and drag diagonally down onto the image. A set of cross hairs appears, marking the new origin on the rulers. The new zero origin will be set where you release the mouse button.
To change the rulers’ settings, double-click a rule, or choose Photoshop Elements > Preferences > Units & Rulers. For Rulers, choose a unit of measurement. For Column size, enter values for Width and Gutter. Click OK.
Some layout programs use the column width setting to specify the display of an image across columns. The Image Size and Canvas Size commands also use this setting.