To get negative values in stacked bars, we combine a first series with all positive values, with two other series with all negative values. First two series are like centered on each side of the main axis. While the last series values are added on top on the second series bars. Centered bars are in fact a particular case of a two-series stacked bar chart, one of them with all positive, the other with all negative values. Get rid of the third series here, and you will find our typical centered stacked bar series chart.