When youre designing a page or setting out items in Photoshop its sometimes helpful to have the rulers to help mark distance or starting points. By default the 0,0 point is set to the top left corner but this can be changed;
Viewing Rulers and Setting the Units
To view rulers press Ctl+R (PC) or Cmd+R (MAC) or choose Rulers from the View menu.
The units of the ruler is set in the preferences but there’s no need to go back there if you wish to change them. Move your mouse onto either the vertical or horizontal ruler and right click. From the pop-up menu choose the units you wish.
Move the 0,0
To reposition the 0,0 point click the mouse in the blank square in the top left corner where the rulers meet and drag the point to where you’d like it.
Guides, HUD and the 0,0 point
This can be a great help to set a starting point for setting out guides as the heads up display offers a reading from the 0,0 point. To make a new guide, click on a ruler and drag a guide onto the document.
New Guides From the Menu
Setting a guide from the menu (View > New Guide) will still take its reference from the top left as 0,0
Resetting the Rulers
You can keep changing the 0,0 point as much as you wish. This works great for setting out contact sheets or web designs.
To reset the 0,0 point to the top left double click on the empty square in the top left where the rulers meet.