To chart comparison values or to combine two related indicators on the same chart, you may need to compensate for different numeric scales. For line, clustered bar, and combination charts, you can use a second Y-axis to represent values on a scalar function that differs from the scale of the first y axis.
For example, you might like to chart the sales of your two fastest growing product lines together to get an idea of how business is growing. However, while the growth rates are similar, the two product lines may sell at entirely different volumes. The chart does not provide much comparative information because each line needs to be charted at a different scale. By using different scales for the two y axes, you can correctly scale each value for the most effective presentation of the data.
To use a different scale for a value on the second y axis, double-click the one of the two values in the y pane in the data layout.
Interactive Reporting changes he scale of the y axis for the value automatically, and italicizes the value name in the data layout. Double-click the item again to return the scale to its default setting.