What is also informative is to overlay similar airfoils, with the 'y' scale expanded 3:1, and look at the differences in contour.
Such as these.... Clark-Y, 3021 and 7037.
And contemplate how precisely you are capable as a builder to build any profile to the exact contour selected.
And then contemplate how your typical wing deviates from perfect, and flies acceptably.
Which leads to... could you detect -any- difference in performance between say the 3021 and 7037, when built to your standards?

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http://www.angelfire.com/indie/aeros...Airfoils01.jpg