All techniques
Axis crimes
Dual y-axes
Two axes, one narrative, infinite flexibility.
a.k.a. secondary axis · the axis of evil
Put one series on the left axis and another on the right, and you get two free knobs to turn until the lines cross exactly where the story needs them to. The correlation you “see” is a design decision, not a finding.
How to spot it
- Two different units share one chart.
- The axis ranges look hand-picked so the lines touch, cross, or track each other.
- Rescale either axis in your head and the drama evaporates.
The fix
Index both series to a common baseline (like % change from a start date), or just use two small charts side by side.
