When the points on such a diagram closely define a straight line you can draw a "so-called" best fit straight line through the cluster. As a cluster of points begins to spread out (like a buckshot pattern) you would have to resort to a formal procedure to obtain the equation of the straight line that "best fits" the pattern.

Take a few minutes an read about The Art of Predicting.

Carefully place the edge of a piece of paper on the screen so that the edge goes through as many o the points as possible.

Estimate the discharge when the stage is 11 feet.

about 9,000 cfs
about 8,000 cfs
about 10,000 cfs

about 3,000 cfs
about 2,500 cfs
about 2000 cfs

Remember that stage is easier to measure than discharge. Therefore, a predicting equation for estimating discharge from stage may save the costs involved in making measurements of discharge. The closer the points are to defining a straight line, the more successful the predicting equation will be. Extrapolation beyond the limits of the data should be avoided. There is no guarantee that a linear relationship exists beyond the limits of the data. (See the first question on this page.)

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