I have searched far and wide for a good definition of portfolio historical relative volatility. I started by looking at the standard mathematical definition of volatility and proceeded to research and analyze Beta, modified Sharpe, Sortino and Treynor ratios and the daily historical volatility that they measure for various mutual funds. After playing around with these and several other definitions from Modern and Post Modern Portfolio Theories I came to the realization that none of these measures, no matter how sophisticated and computationally intensive, gave me what I was really after.