Why should volume readings be taken with the eye level parallel to the meniscus?
Answer:
To prevent parallax errors - that is an over or underestimation of the volume level should the menicus not be read perpendicularly.
Because looking down at it or up at it will simply give you a false reading. It will look like the line is at a different place than it actually is.
because the miniscus is at the center of the measurment tool and not at the edge, if you look down at the miniscus, you will see that it aligns with a different value than if you look up at it. The best way to avoid innaccurate measurements is to keep your eye level with it.
This is to prevent parallax error and to avoid inaccurate measurements as the meniscus of water is a curve.
One should observe the reading that is parallel to eye level.
The main reason is to permit consistency and repeatability because everyone can get the very same measurement by the method you cite. The meniscus of water and mercury are opposite curves and the meniscus also depends upon the diameter of the glass tube due to capillary action. If 100 cc's of a chemical (measured using the meniscus) proves to be exactly the amount required, you don't want someone else to measure 100 cc's by their own method.
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