Dual axis

A chart with two value axes, one on the left and one on the right, allowing two series of different units to be plotted on the same chart. Dual-axis bar charts are tricky: readers often don't notice the second axis and misread one series's values. When possible, use two stacked charts (small multiples) instead. If you must use dual axis, label both axes prominently and color-code the bars to match each axis.