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Tuesday, July 15, 2008

Measuring distance

Make a point on a piece of paper and place it in front of you on the table. Now try to hit the point with a pencil held in your hand. You will manage it easily. But if you close one eye, you will almost always miss your target.

The distance can only be estimated with difficulty with one eye, because one normally sees a composite image with both eyes and so can discern the depth of a space. Each eye stares at the point from a different angle (notice how the angle alters if you move nearer to the point). The brain can then determine the distance of the point fairly accurately from the size of the angle.

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