What indicates what time periods are represented by each successive data point on a graph?

The horizontal axis label is essential because it directly informs the viewer of what time periods correspond to the successive data points plotted on the graph. This axis typically represents the passage of time, allowing observers to understand trends and patterns over different intervals effectively. By providing clarity on the scales of measurement along the time continuum, the horizontal axis helps in interpreting how the data points relate to each other as time progresses.

In contrast, while data markers represent individual data points on the graph, they do not specify what time periods they signify. The legend serves to explain the various lines or symbols used in cases where multiple datasets are represented but does not denote time periods. The title of the graph gives a general overview of what the graph is about but lacks the specifics necessary to understand the timing of the data points. Hence, the horizontal axis label is the key component that indicates the time periods associated with the data plotted.