models/classes/runner/time/QtiTimer.php
public function compute($tags, $target)
    {
        // cannot compute a duration across different targets
        if (!$this->onlyOneFlag($target)) {
            throw new InconsistentCriteriaException('Cannot compute a duration across different targets!');    
        }
        
        return $this->timeLine->compute($tags, $target);
    }
public function compute($tags, $target)
    {
        // cannot compute a duration across different targets
        if (!$this->onlyOneFlag($target)) {
            throw new InconsistentCriteriaException('Cannot compute a duration across different targets!');    
        }
        
        return $this->timeLine->compute($tags, $target);
    }
Computes the total duration represented by the filtered TimePoints
@param string|array $tags A tag or a list of tags to filter
@param int $target The type of target TimePoint to filter
@return float Returns the total computed duration
@throws TimeException