In my tutorial on jpeg quality, I displayed two photos side by side and zoomed in on them together to compare them up close. A reader asked me how I did this — thanks to this reader for giving me the idea for Friday’s Lightroom Quick Tip.
In the Library module, select your two photos (click on the first, Ctl/Cmd-click on the second). Then, in the toolbar below the grid, click on the X/Y button — this is Compare view. The shortcut “C” also works.