public function toDays($d)
    {
        $v = $this->getValue();
        return $d/($this->c6/$this->{'c'.$v});
    }
public function toDays($d)
    {
        $v = $this->getValue();
        return $d/($this->c6/$this->{'c'.$v});
    }
public function toDays ( $ d ) { $ v = $ this -> getValue ( ) ; return $ d / ( $ this -> c6 / $ this -> { 'c' . $ v } ) ; }
Convert to days

@param int $d
@return float
Convert to days