public function calculate()
	{
		$sum		= 0;
		$arguments	= func_get_args();
		for( $i=$this->interval->getStart(); $i<=$this->interval->getEnd(); $i++ )
		{
			$params	= array( $i );
			foreach( $arguments as $argument )
				$params[]	= $argument;
			$value	= call_user_func_array( array( &$this->formula, 'getValue' ), $params );
			$sum	+= $value;
		}
		return $sum;
	}