https://blog.gongquiz.com/2022/11/24/%eb%8b%a4%ec%9d%8c-%ec%a4%91-%eb%a7%a5%ed%8c%8cpulse-wave%ec%9d%98-%ec%a2%85%eb%a5%98%ea%b0%80-%ec%95%84%eb%8b%8c-%ea%b2%83%ec%9d%80-%ec%9d%98%ea%b3%b5%ea%b8%b0%ec%82%ac-2008%eb%85%84-9%ec%9b%94/