Sets or returns the formula to use to calculate the value for the text item. For example, if the formula is "=Sheet1!A1", the value in that cell will be the text displayed in the ChartText object.

(This has no meaning for SeriesDataLabel on a series or on a data point.)

public System.String Formula{ get; set; }
Public Property Formula() As String

The formula may be a reference to a cell, range of cells, or a union of such references.