A comparison microscope is a specialized microscope that allows for a side-by-side comparison of different materials. Invented by Calvin Goddard in the 1920s, these microscopes are often used today by the FBI and other law enforcement to determine the similarities of objects such as hairs and fired ammunition.
Comparison microscopes are essentially two separate microscopes connected by a bridge that includes a single viewing lens. Two similar objects can be placed on the opposing stages and be viewed simultaneously in the same viewing field. This greatly assists examiners in comparing two like materials without the need for moving between two separate microscopes.