Distance offset and zoom behaviour

The Heightgraph provides a great overview even for long tracks of several 100km. However, local details of this track may be of interest but are not visible as their length is short compared to the graph.
An thinkable option to circumvent this could be to create a second Heightgraph window which shows the graph for the selected area only (maybe there are much better solutions).
To realise this, two options would be nice to have when initialising Heightgraph:
1. provide an offset for the distance axis, e.g. to start counting the distance with 112.5km.
2. provide a callback function when _dragEndHandler is called. It could supply the distance values where the zoomed area starts/ends or even provide a geojson of the selected track segment which could be fed into the second instance of Heightgraph where the distance offset is applied.