Visualization information about graph dots

It should be possible to get information about each point of a graph.

1. When a mouse is moved in the Graphs area, a small circle should be shown on the graph (i.e. only X axis of mouse move is taken into account). A coordinates hint should be also shown, for example, above it.
2. When a user holds Shift and clicks on a graph, the circle and the hint should be locked. The second circle should appear in case of mouse move in the Graphs area.
3. It should be possible to create as many locked circles+hints as user would like to.
4. When a user clicks on a locked circle, the circle+hint should be removed.