Originally Posted by Mr. Deer Hunter

I'm sorry here but you people do not know what you are talking about.

Parallax is the difference between where you are looking and where the actual bullet is pointed towards. Parallax also affects optical instruments such as binoculars, microscopes, and twin-lens reflex cameras that view objects from slightly different angles. Many animals, including humans, have two eyes with overlapping visual fields to use parallax to gain depth perception; this process is known as stereopsis.
A simple everyday example of parallax can be seen in the dashboard of motor vehicles that use a "needle" type speedometer gauge (when the needle is mounted in front of its dial scale in a way that leaves a noticeable spacing between them). When viewed from directly in front, the speed may show 60 (i.e. the needle appears against the '60' mark on the dial behind); but when viewed from the passenger seat (i.e. from an oblique angle) the needle can appear against a slightly lower or higher mark (depending on whether it is viewed from the left or from the right), because of the combined effect of the spacing and the angle of view.

As the eyes of humans and other animals are in different positions on the head, they present different views simultaneously. This is the basis of stereopsis, the process by which the brain exploits the parallax due to the different views from the eye to gain depth perception and estimate distances to objects