Annotate a chart only with a fact from outside the dataset that explains it - a rainy day, a regulation, an acquisition, a change of government. Use when a chart needs an on-chart mark for an external cause, an event, or a regime change the data itself cannot show. In-data quantities - "peak", "all-time high", "from X to Y", a rank, a trend, a crossover - are direct labels, not annotations; this skill also words and places those. Also use when annotation text is too long, too many marks compete, the mark repeats the title, or a number is not tied to a baseline.
