*/
@Override
public Number getStartValue(Comparable series, Comparable category) {
int seriesIndex = getSeriesIndex(series);
if (seriesIndex < 0) {
throw new UnknownKeyException("Unknown 'series' key.");
}
int itemIndex = getColumnIndex(category);
if (itemIndex < 0) {
throw new UnknownKeyException("Unknown 'category' key.");
}
return getStartValue(seriesIndex, itemIndex);
}