In this post, we are going to discuss historical volatilities of a stock in more details. There are various types of historical volatilities such as close to close, Parkinson, Garman-KIass, Yang-Zhang, etc. Here we will discuss the close-to-close historical volatility. It’s observed that the volatility is a mean-reverting process.

http://tech.harbourfronts.com/trading/close-close-historical-volatility-calculation-volatility-analysis-python/