Often mentioned on forensic-based TV cop-shows, but rarely actually shown , Comparison Microscopes are excellent tools not just for forensic work, but also for comparing different tissue types, teaching, and for checking diseased vs. healthy tissues. They are used to compare the samples on two slides side-by-side.
They look clunky, because they essentially are just two microscope bodies attached a the top by an optical bridge. The mechanics are 2 high quality binocular microscopes which combine 4 DIN objectives (or 5 in the advanced model), a large stage, a mechanical stage, coarse & fine focus, and N.A. 1.25 Abbe Condensers among many other features.
To do a comparison of slides, you place 1 slide on each stage, bring them to focus, and make adjustments on the optical bridge.
The resulting image shows the samples side-by-side. Here is one example of a human stomach cell side-by-side with a human kidney cell:
Comparisons can be made with almost anything that can be put on a slide. Comparison Microscopes are invaluable in teaching students to see diseased tissues vs. healthy, forensic work, and a host of other fields.