public function getValue()
    {
      $value = sprintf("%02d:%02d", $this->hours, $this->minutes);
      
      if(isset($this->seconds))
        $value .= sprintf(":%02d", $this->seconds);
        
      if(isset($this->microtime))
        $value .= substr($this->microtime, 1);
          
      return $value;
    }