Hi there! In Acrobat, the rulers used to change size based on the Custom Resolution setting. I'm not sure when this broke, but it's not working anymore. Now when you change the Custom Resolution setting, the ruler stays the same size and does not measure accurately, compared to the Measure tool which does measure accurately.

For an example, see the screenshot. In Preferences / Page Display / Resolution, the system setting is 111, but if I change it to 130 so that pages display larger at 100% resolution, the size of the ruler does not change. When I use the measure tool, it measures a length of 6.08 inches, but the onscreen ruler right next to it says that it is 7 inches.

Based on the document size, that 6.08 inches measurement is accurate and the 7 inches on the onscreen ruler is wrong. So that is a bug.

Next, a related feature request: For my screen, I really want to set the custom resolution to 112.5, so a physical ruler held up to the screen would give accurate measurements at 100% display size. Unfortunately, the Custom resolution field only takes integers. It would be great if I could use a decimal in that field.