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How to Prevent Parallax Error

By Karl Wallulis; Updated April 30, 2018

Parallax error occurs when the measurement of an object's length is more or less than the true length because of your eye being positioned at an angle to the measurement markings. For example, a person viewing a car's speedometer from the driver's seat will get an accurate reading because she has a direct line of sight. A person viewing the speedometer from the passenger seat will overestimate the reading because of the angle between his eye, the meter and the arrow.