The current 1:1 (Zoom to 100%) button in the ArcMap layout view should display your page and map as if it were "taped" to your screen. The rulers displayed on your screen should match a ruler placed against your monitor. It should be like looking at your actual printed map on your monitor. Instead, the current button actually displays less than 100% making the layout shown on your monitor slightly smaller than the printed map. If you want to see your layout as it would look printed, you have to compensate by displaying the layout not at 100% or 1:1, but more like 108%. There is value to this button (1:1) if it really does display your map as if it were "taped" to the monitor...not so much if it doesn't.