Bug 212370 [Regression] Negative value can not be shown both in chart builder and when preview [13]
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/computation/withaxes/AxisSubUnit.java
{
			
			this.dValueLast += dValue;
		}
		else
		{
			if ( dValue > 0 )
			{
				
				this.dValueLast += dValue;
			}
			else if ( dValue < 0 )
			{
				
				this.dValueLastNegative += dValue;
			}
		}
		return getStackedValue( dValue );
	}
	/**
	 * Returns the current accumulated value.
	 * 
	 * @param dValue
	 *            value to check the sign. If stack together, it's no use.
	 * @return the current accumulated value.
	 */
	public final double getStackedValue( double dValue )
	{
		if ( bStackTogether )
		{