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8.1.4 Adding a second Y-scale

As you saw in the preceding example you could add multiple plots to the same graph and Y-axis. However what if the two plots you want to display in the graph has very different ranges. One might for example have Y-values like above but the other might have Y-values in the 100:s. Even though it is perfectly possible to add them as above the graph with the smallest values will have a very low dynamic range since the scale must accomplish the bigger dynamic range of the second plot.

The solution to this is to use a second Y-axis with a different scale and add the second plot to this Y-axis instead. Let's take a look at how that is accomplished.

First we need to create a new data array with large values and secondly we need to specify a scale for the Y2 axis. This is done by the lines

 $y2data = array( 354,200,265 ,99,111, 91,198,225 ,293,251);
$graph->SetY2Scale( "lin");

and finally we create a new line plot and add that to the second Y-axis. Note that we here use a new method, AddY2(), since we want this plot to be added to the second Y-axis. Note that JpGraph will only support two different Y-axis. This is not considered a limitation since using more than two scales in the same graph would make it very difficult to interpret the meaning of the graph.

To make the graph a little bit more esthetic pleasing we use different colors for the different plots and let the two different Y-axis get the same colors as the plots.

The resulting graph is shown below. source)

Figure 10: Adding a second Y-scale plot to the same graph [src] 

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