Rulers is an innovative screen rulers application specifically for Mac OS X. Features of Rulers include:
Moveable: rulers can be moved around the screen.
Resizeable: rulers can be stretched and shortened.
Lockable: horizontal and vertical rulers can be "locked" so that they move together.
Opacity: rulers can be set fully opaque, or set semi-transparent so you can see through to underlying content.
Origins: ruler origins---that is, zero point---can be set to left or bottom, middle, or right or top.
Shift: rulers can be shifted to the edges of the screen.
Units: units include sixteenths or tenths of inches, Picas, Points, Centimetres, Millimetres, Pixels, and Percentage of Length.
Scale: Scale factors include 100 percent (one for one), 200 percent, 50 percent, 127 percent, and 78 percent.