public function toMicros($d)  
    {
        $v = $this->getValue();
        if ($v < self::MICROSECONDS) {
            return $d/($this->c1/$this->c0);
        } else {
            return $this->x($d, $this->{'c'.$v}/$this->c1, PHP_INT_MAX/($this->{'c'.$v})/$this->c1);
        }
    }