Trendline Object [Excel 2003 VBA Language Reference]
Represents a trendline in a chart. A trendline shows the trend, or direction, of data in a series. The Trendline object is a member of the Trendlines collection. The Trendlines collection contains all the Trendline objects for a single series.
Using the Trendline Object
Use Trendlines(index), where index is the trendline index number, to return a single Trendline object. The following example changes the trendline type for the first series in embedded chart one on worksheet one. If the series has no trendline, this example will fail.
Worksheets(1).ChartObjects(1).Chart. _ SeriesCollection(1).Trendlines(1).Type = xlMovingAvg
The index number denotes the order in which the trendlines were added to the series.
Trendlines(1) is the first trendline added to the series, and
Trendlines(Trendlines.Count) is the last one added.