Garman-Klass Volatility (original)

Compute the original Garman-Klass volatility of an asset over a given time period, using open, high, low and close prices.

References

• Colin Bennett, Trading Volatility, Correlation, Term Structure and Skew
• Garman, M. B., and M. J. Klass, 1980, On the Estimation of Security Price Volatilities from Historical Data, Journal of Business 53:67–78