TTChartOnCalendarSeriesChange

type TTChartOnCalendarSeriesChange = procedure(ASender: TObject; Series: Integer; Value: Double) of object;

Type Library
TeeChartx

Description
The TTChartOnCalendarSeriesChange event notifies that the end-user has clicked on a

different calendar day.

The Value parameter specifies the new day. You have the opportunity to modify

this value thus overriding the user day change.