Currently, the Chart does not have events related to zooming in and out using selection, so it is not possible to tell if the Chart is currently being zoomed using selection. An alternative approach to allow zooming with a Chart using realtime updates would be to render the zoom UI outside the Chart, for example zoom in and zoom out buttons, like shown in this example:
As for the crosshair, it can be shown only internally by the Chart at this point, so restoring it at the position where it was last shown before the Chart refresh is not possible. I am sorry for the inconvenience caused by this.
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