Parallax is an apparent 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.
Let me quote an example of paralla, Once, I was driving and my father informed me the tank was on empty. I told him that, no, I had plenty of gas -- a good quarter tank left. He leaned over and, looking straight at the gas gauge, said "ah... A Parallax Problem.
Hope this helps.
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