protected double calculateSeriesWidth(double space, CategoryAxis axis,
                                          int categories, int series) {
        double factor = 1.0 - getItemMargin() - axis.getLowerMargin()
                            - axis.getUpperMargin();
        if (categories > 1) {
            factor = factor - axis.getCategoryMargin();
        }
        return (space * factor) / (categories * series);