The bore axis of a firearm is the longitudinal axis through the geometric center of the gun barrel. In a rifled barrel, the projectile will spin around the bore axis as it goes through the barrel.
The AR-15 is an example of a weapon system where the sights are high over the bore.
Browning BAR is an example of a weapon system where the sights sit low and close to the bore.
The Chiappa Rhino is an example of a pistol with a low bore axis.
The Sig Sauer P226 is an example of a pistol with a high bore axis.
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or half-angle of inclination between those two lines. Due to foreshortening, nearby objects show a larger parallax than farther objects, so parallax can be used to determine distances.
In this photograph, the Sun is visible above the top of the streetlight. In the reflection on the water, the Sun appears in line with the streetlight because the virtual image is formed from a different viewing position.
Parallax measurements may be an important clue to understanding three of the universe's most elusive components: dark matter, dark energy and neutrinos.
Hubble Space Telescope precision stellar distance measurement has been extended 10 times further into the Milky Way.
Contax III rangefinder camera with macro photography setting. Because the viewfinder is on top of the lens and near the subject, goggles are fitted in front of the rangefinder and a dedicated viewfinder is installed to compensate for parallax.
