SerialDataItem holds all the information about each series. When working with a chart, you do not create SerialDataItem objects or change it's properties directly. Consider properties of a SerialDataItem read-only - change values in chart's data provider if you need to. When serial chart parses dataProvider, it generates "chartData" array. Objects of this array are SerialDataItem objects.
You can access each GraphDataItem using this object. The data structure is: graphDataItem = serialDataItem.axes[axisId].graphs[graphId].
category value. String if parseDates is false, Date if true.
Timestamp of a series date. Avalable only if parseDates property of CategoryAxis is set to true.
Coordinate (horizontal or vertical, depends on chart's rotate property) of the series.