Start by stating what the index does: it lets you compare relative change from a common base, not absolute size across series.

That distinction matters because a line at 130 means the metric increased 30 percent from its own base, not that it is larger than another series at 120 in absolute terms.

Use the chart to compare growth rates, inflection points, and divergence over time, while avoiding unsupported statements about absolute revenue, volume, or market size.

If absolute scale matters for the decision, explicitly ask whether the underlying base values are available. For a related reference, see case interview exhibits.

I would practice this with a timer. The pressure changes the way you respond more than the actual concept does.