Stacked charts are charts that have one or more series stacked upon a base series. All of the Y values for the chart are taken as distances from the previous series’ Y value. Stacked charts are a simple issue when data is loaded in an array format where the X values all match and all the series are stacked on top quite neatly. 

C1Chart provides more freedom by allowing data to be in a General Layout. General Layout means that not all series must have identical X values. While this freedom allows for charting of more non-standard sets of data, it poses a problem when using stacked charts.