procedure TfrmGraph.DBChart1ClickSeries(Sender: TCustomChart;
  Series: TChartSeries; ValueIndex: Integer; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);

begin
 Sender.Hint :='';
 Sender.Hint := Series.YValues.ValueSource + # 13 # 10 +
                'Date and Time :'+ Series.XValueToText(Series.XValue[valueindex])  +# 13 # 10 +
                'Value: ' + Floattostr(Series.YValue[valueindex]);
 Sender.ShowHint := True;
end;