Comparison charts are very common and most important charts for any data. Tableau also can create some very special comparison charts. One such widely used and popular chart in excel and other BI tools is a Dual Axis Chart or referred to as Combo Chart (Involves the combination of 2 charts).
We focus on 2 measures where one measure is superimposed over another measure. Many of us assume that the second measure is placed above the first measure. It is not above, it is on (One behind another).
Any other comparison chart that we build in Tableau needs the same scale for comparison. But Dual Axis (The word itself is very intuitive – 2 Axes: one for each measure) allows for the use of different measures. In many cases, Dual Axis is used for Time Series.