A second y-axis is useful for plotting data with different scales on the same plot, such as a stock’s closing price and its daily volume, or temperature and pressure. For example, consider plotting the selling price of an inexpensive stock against the Dow Jones Industrial Average.
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Click OK.
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From the red triangle menu for Overlay Plot, select Y Options > Connect Points.
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Figure 4.9 Dual Axis Overlay Plot
The variables High, Low, and Close are the stock prices of the same stock and thus are on the same scale. Volume is a different scale entirely, representing the trading volume of the entire Dow Jones Industrial Average.
To see why this matters, perform the same steps above without clicking the Left Scale/Right Scale button for Volume. Compare the resulting graph in Figure 4.10 to Figure 4.9.
Figure 4.10 Single Axis Overlay Plot
