public function toFormattedString()
    {
        switch (self::$format) {
            case 'full':
                return number_format($this->num, 0, ',', '.') . '-' . $this->vd;
            case 'basic':
                return $this->num.'-'.$this->vd;
            case 'raw':
            default:
                return $this->num.$this->vd;
        }
    }