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 semi-angle of inclination between those two lines. Parallax is most common when reading markings on measuring instruments.
A simple everyday example of parallax can be seen in the dashboard of motor vehicles that use a needle-style non-LCD speedometer gauge. When viewed from directly in front, the speed may show exactly 60, but when viewed from the passenger seat, the needle may appear to show a slightly different speed, due to the angle of viewing (source).
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