When data set you are comparing in excel varies too much, graphical comparison becomes difficult. A Secondary axis can easily be inserted in chart using inbuilt options of excel.
Sample chart below is having two data set and its clearly visible that input data is hardly visible. Here we can use an secondary axis.
Insert Secondary axis
- Select data and create a chart.
- Right click on format data series. Select Secondary axis.
- Now right click on series with larger values. Select change series type. Change to line type for this series.
Final Chart will look like this