A comparison microscope or stereomicroscope or dissecting microscopes are a device used to analyze side by side specimen. It consists of two microscopes connected to an optical bridge that results in a split view window. The comparison microscope is used in forensic sciences to be able to compare microscope patterns and identify or deny their common origin. There are two microscopes that are placed next to each other and the optical paths of each microscope that are connected together by the optical bridge would help the forensic examiners to simultaneously compare two specimens instead of depending their memory are the simple idea behind the comparison microscope. Handguns predominated as the firearm of choices in shooting-related crimes, especially in the United States of America. The fired ammunition components may acquire sufficient unique and reproducible microscopic marks to be identifiable as having been fired by a single firearm.

A correctly referred to as firearms identification or sometimes called as ballistic is in the making of this comparison. The forensic discipline ultimately requires a microscopic side by side comparison of fired bullets or cartridge cases, one pair at a time, by a forensic examiner to confirm or possibly eliminate the two items as having been fired by a single firearm. The traditional tool of the firearms examiner has been what is often called the ballistic comparison microscope. An essential for the forensic ballistic expert in comparing bullets and spent cartridge casing is a comparison microscope. The interior of a gun’s barrel is machined to have grooves that force the bullet to rotate as it travels along it.  These grooves and their counterpart, called lands imprint groove and land impressions on the surface of the bullet. Imperfections on the barrel surface are incidentally transferred to the bullet’s surface.

They are unique to each barrel since these imperfections are randomly generated. These patterns or imperfections amounts to a signature that each barrel imprints on each of the bullets fired through it. It is this signature on the bullets imparted due to the unique imperfections on the barrel that enable the validation and identification of bullets as having originated from a particular gun. The comparison microscope is used to analyze the matching of the microscopic impressions found on the surface of bullets and a casing. Forensic examiners compare the ballistic fingerprint of the recovered bullet or cartridge case with the ballistic fingerprint of  second bullet or cartridge case test fired from the recovered firearm is when a firearm or a bullet or cartridge case are recovered from  crime scene. If the ballistic fingerprint on the test fired bullet or cartridge case matches the ballistic fingerprint on the recovered bullet or cartridge case matches the recovered bullet or cartridge case was also fired from the recovered gun. A link between a specific firearm and a bullet or cartridge case recovered from a crime scene constitutes a valuable lead, since investigators may be able to connect the firearm to a person, who may then become either a suspect or a source of information helpful to the investigation.