The fly-over should not only activate on hover. It should present itself when a highlightable portion of a chart is selectable. On mobile, a user should be able to tap on a portion of the graph to make it appear.
The fly-over is not always necessary but is recommended unless there’s another piece of the UI that highlights the selected data and ties those two things together.
The flag is Peppercorn at 90% opacity. It should be centered at the data it points to and pinned to the highest reasonable point of a chart.
The pole is Peppercorn at 100% opacity and should be centered to the flag. In cases where the fly-over is near the edge of a chart, you may adjust the positioning of the flag on the pole.
If the chart has fewer than two items to call out, you may eliminate the pole and just use the flag.