Hi Irina,
Yes you can use relative units to specify the size of the header - for example:
nChartControl1.Panels.Clear();
NLabel label = new NLabel("Some Label");
label.BoundsMode = BoundsMode.Fit;
label.TextStyle.FontStyle.EmSize = new NLength(5, NRelativeUnit.RootPercentage);
label.DockMode = PanelDockMode.Top;
nChartControl1.Panels.Add(label);
NCartesianChart chart = new NCartesianChart();
chart.DockMode = PanelDockMode.Fill;
nChartControl1.Panels.Add(chart);
NBarSeries bar = new NBarSeries();
bar.Values.Add(10);
bar.Values.Add(20);
bar.Values.Add(30);
chart.Series.Add(bar);
Alternatively you can simply set the font size depending on the export image size.
Best Regards,
Nevron Support Team