A lot of designers prefer doing sketches before heading to Photoshop or Illustrator. Creating things to scale can often be tricky, and converting centimeters to pixels isn’t exactly something most can do freehand. UI Stencils has created the Pixel Ruler, a stainless steel ruler that has markings in pixels up to 1700 pixels, at a scale of 150 PPI.
Such a great idea. Hopefully UI Stencils releases some alternatives based on various PPIs in the future.