Each weekday, TheStreet.com Ratings updates its ratings on the stocks it covers. The proprietary ratings model projects a stock's total return potential over a 12-month period, including both price appreciation and dividends. Buy, hold or sell ratings designate how the Ratings group expects these stocks to perform against a general benchmark of the equities market and interest rates. While the ratings model is quantitative, it uses both subjective and objective elements. For instance, subjective elements include expected equities market returns, future interest rates, implied industry outlook and company earnings forecasts. Objective elements include volatility of past operating revenue, financial strength and company cash flows. Gerdau Ameristeel ( GNA) operates as a minimill steel producer in North America. It has been upgraded to a buy from a hold. The company's revenue grew by 10.4% in the second quarter compared with the same period last year, and its debt-to-equity ratio of 0.22 is below that of the industry average, implying that there has been very successful management of debt levels. Gerdau's stock price has risen by 23.33% over the last 12 months, outpacing the rate of the S&P 500. While it goes without saying that even the best stocks can fall in an overall down market, in any other environment, this stock still has good upside potential. Gerdau had been rated a hold since September 2007. Biopharmaceutical company ImClone Systems ( IMCL) engages in the development and commercialization of a portfolio of targeted treatments for cancer patients. It has been upgraded to a buy from a hold. The company's stock price has improved by 50.81% in the past 12 months and should continue to move higher. Net operating cash flow increased by 193.32% to $27.34 million when compared with the same period last year. ImClone also displays reasonable valuation levels and a largely solid financial position with reasonable debt levels by most measures. These strengths outweigh the company's subpar growth in net income. ImClone had been rated a hold since July 2007.