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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.
1.
Select Help > Sample Data Library and open Stock Prices.jmp.
2.
Select Graph > Legacy > Overlay Plot.
3.
Assign High, Low, Close, and Volume as Y variables.
4.
Select Volume in the Y list and click Left Scale/Right Scale.
5.
Assign Date as the X variable.
6.
Figure 5.9 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 5.10 to Figure 5.9.
Figure 5.10 Single Axis Overlay Plot

Help created on 3/19/2020