Over the weekend, I completed three articles, all on the same topic: the correlation coefficient between stock returns and changes in implied volatility. This is the first introductory article, which details the variable definitions and calculation methods. Using $Tesla(TSLA.US) as an example, it demonstrates how the correlation coefficient can serve as a reference for judging stock price bottoms. The underlying logic is that during the mid-to-later stages of a stock's wave-like decline, it often triggers panic among market participants, leading to irrational buying of put options at higher prices.