It would be extremally useful to my workflow to have the ability to set scale in the canvas app with a known dimension (ruler would be welcome to the screen annotation as well) and have that scale relate to a ruler which could be brought up on the screen so one can sketch to scale in a canvas. We are using our vibe for redlining pdf sets of drawings and often need to be able to sketch to scale / have a sense of how big a room or building element is. A program called morfolio trace we use all the time on the ipad does a great job with this and feels like it would be right at home in the canvas environment.