A dual axis time series plot is a variation of the time series plot that has two measures.
A measure is displayed on both the left and right side of
the Y axis.
For example, a dual axis time series plot can be useful when you need to display two
measures that have the same unit of measurement
and different scales, such as quantity ordered and returns, or when you need to display
two measures that have different units of measurement, such as sales and quantity
ordered.