Revisiting this issue, while it is true that the same series object cannot be added to two different charts, it is also true that the same Arrays can be used by two series each in two different charts, e.g.:

    double[] XValues, YValues;
	
	private void button1_Click(object sender, EventArgs e)
    {
      YValues[1] = 7;

      ModifySeries(tChart1[0]);
      ModifySeries(tChart2[0]);
    }

    private void InitializeChart()
    {
      tChart1.Aspect.View3D = false;
      tChart2.Aspect.View3D = false;

      XValues = new double[] { 1, 2 };
      YValues = new double[] { 1, 2 };

      AddNewSeries(tChart1);
      AddNewSeries(tChart2);
    }

    private void ModifySeries(Series series)
    {
      series.YValues.Modified = true;
      series.XValues.Modified = true; 

      series.Invalidate();
    }

    private void AddNewSeries(TChart tChart)
    {
      FastLine series1 = new Steema.TeeChart.Styles.FastLine(tChart.Chart);
      series1.YValues.Value = YValues;
      series1.YValues.Count = YValues.Length;

      series1.XValues.Value = XValues;
      series1.XValues.Count = XValues.Length;
    }

would only need to modify one set of arrays and then call ModifySeries for each of his series to propagate the new data through all of his charts. Is this sufficient?

The trick here is that, as it says at http://msdn.microsoft.com/en-us/library/9b9dty7d.aspx, "Array types are reference types derived from the abstract base type Array." As reference types (http://msdn.microsoft.com/en-us/library/490f96s2.aspx), "two variables can reference the same object; therefore, operations on one variable can affect the object referenced by the other variable.". This can be seen with this example:

    double[] Array, CopyArray;

    private void InitializeChart()
    {
      Array = new double[] { 1, 2 };
      CopyArray = Array;
        
    }
    private void button1_Click(object sender, EventArgs e)
    {
      Array[1] = 7;
      MessageBox.Show(CopyArray[1].ToString());
    }