Building one
Put the first measure on Rows. Drag the second to the opposite edge of the view until a black dashed line appears, or right-click the second pill and choose Dual Axis.
Each measure then gets its own Marks card, so one can be bars and the other a line — the standard actual-against-target chart.
Synchronise
With unsynchronised axes you can position two series to suggest almost any relationship, deliberately or not.
If both measures share a unit, right-click the secondary axis and Synchronise Axis. If they do not share a unit, keep them separate but label both axes clearly.
Where the measures share a unit and a similar range, a blended axis — dragging the second measure onto the first axis — is more honest still, because one shared scale removes the question entirely.
Combination marks
The per-measure Marks card is what makes combination charts possible:
- Bars for actuals, line for target
- Line for the trend, circles for the individual points
- Area for volume, line for the rate
Select the Marks card for a measure and change its type independently.
Dual axis for shapes and maps
The technique is not only for two measures. Duplicating a measure and setting a dual axis lets you layer two mark types on the same data — circles behind bars for a lollipop chart, or symbols over a filled map.
For maps specifically, duplicating Latitude on Rows and setting a dual axis is how you put symbol marks on top of a filled map.