On the vertical axis of each graph is the probability of autism.

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On the horizontal axis of each graph, we have total traffic-related air pollution exposure, increasing in parts per billion (a part here would be a drop in a billion drops) from left to right.

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And, as Euler's successor, Carl Friedrich Gauss, was to discover, if you plot real numbers on one axis of a graph and imaginary ones on the other, you create a plane that represents both sorts of numbers.

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In the graph below, the Y axis is the citation score and the X axis is the number of publications in total.

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To explain the graph a bit more clearly, the X axis is months and years, while the Y axis is the volume of industrial activity as a percentage of the average monthly output of 2009 (which, it should be noted, was depressed as a result of the global financial crisis).

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