I am looking for a simple formula (easy to code in TC2007 for example) that could help me rank stocks based on the expected volatility. What are good predictors of the next day volatility? According to this http://www.cs.sunysb.edu/~finance/longo/ previous day(s) volatility is a good predictor. So, I should be able to use a crude formula like this: Vol_expected=Vol_yesterday*x+Vol_2days_ago*y+Vol_3days_ago*z . Where do I get estimates for x,y,z parameters? Are there better formulas?