Currently, the real scale calculation done by page_calc_height_width defines the 100% zoom level as "1 point in document" (1/72 inch) = "1 pixel". This MR implements a real scale calculation based on the monitor DPI. 100% zoom is defined as "1 point in document" = "1 point on monitor (physically)". This way, the size of the document on the screen matches the size it would have on paper.
This should fix issue 655.