Thanks a lot it works quite well when put in the "OnBeforeDrawAxes" event, even if it slow a bit then movement of the chart.

Well, now if you could help me with the marks, I would be completely happy.

Sorry to insist. I'd need to know if something can be done.
Having the solution is important but knowing if I have to find another system to manage my charts is even more important, as I'll have to start soon.

I have a TChart on which I build several TGanttSeries and one TLineSeries at run time. Each TGanttSerie represent a step in a production process, each "line" represent one process. So each bars use its step number as a mark and I use LeftAxis.Items to display the correct labels. For <Each Item on th...