Each business day, 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.

However, the rating does not incorporate all of the factors that can alter a stock's performance. For example, it doesn't always factor in recent corporate or industry events that could impact the stock price, nor does it include recent technology developments and competitive dynamics that may affect the company.

For those reasons, we believe a rating alone cannot tell the whole story, and should be part of an investor's overall research.

ARM Holdings

( ARMHY) designs reduced instruction set computing microprocessors, physical intellectual property and related technology and software. It has been downgraded to hold from buy. The company's third-quarter revenue rose by 7.1% compared with the same period last year, which trailed the industry average of 9.5%. ARM Holdings also has a largely solid financial position with reasonable debt levels by most measures. Its return on equity improved slightly in the third quarter compared with the same period last year; this can be construed as a modest strength in the organization. However, the company's stock price has fallen by 14.29% in the last 12 months, and looking ahead, we do not see anything in its numbers that would change the one-year trend. (Naturally a bull or bear market could sway the movement of this stock.) ARM Holdings had been rated a buy since May 2007.

Thor Industries

(THO) - Get Report

manufactures and sells recreation vehicles, small and midsize buses, and related parts and accessories. It has been downgraded to hold from a buy. The company's net income rose 24.9% to $38.21 million, or 68 cents a share, in the first quarter of its fiscal 2008, from $30.60 million, or 55 cents per share, in the same period last year. Thor has reported somewhat volatile earnings recently, but TheStreet.com Ratings believes it is poised for EPS growth in the coming year. However, the company also shows weak operating cash flow and poor profit margins. Its stock price has fallen by 33.65% in the last 12 months. Investors should not assume it can now be tagged as cheap and attractive. Based on its current price in relation to its earnings, Thor is still more expansive than most of the other companies in its industry. Thor Industries had been rated buy since January 2006.

Harry Winston Diamond

( HWD) mines and retails diamonds around the world. It has been downgraded to hold from buy. The company's third-quarter revenue rose 21.5% compared with the same period last year, which trailed the industry average of 36.1%. Its profit margins also expanded. However, it swung to a loss of 13 cents a share from a profit of 32 cents a share a year earlier. Harry Winston Diamond has not demonstrated a clear trend in earnings over the past two years, making it difficult to accurately predict earnings for the coming year. It also has a disappointing return on equity, and its stock price has declined by 24.67% over the past 12 months. Looking ahead, we do not see anything in the company's numbers that would change the one-year trend. Harry Winston Diamond had been rated buy since January 2006.

Quintana Maritime

( QMAR), together with its subsidiaries, provides dry bulk marine transportation services in Greece and internationally. It has been downgraded to sell from hold. The company's debt-to-equity ratio of 1.48 is relatively high when compared with the industry average, suggesting a need for better debt level management. Still, its quick ratio is somewhat strong at 1.04, demonstrating the ability to handle short-term liquidity needs. Quintana Maritime's return on equity is below that of both the industry average and the

S&P 500

. The company's stock price has increased by 33.82% over the past year, but despite these nice gains, TheStreet.com Ratings believes that the risks surrounding an investment in its stock outweigh any potential future returns. The company had been rated hold since November 2007, prior to which it had been rated a sell since coverage was initiated in August 2006.

Additional ratings changes are listed below.

This article was written by a staff member of TheStreet.com Ratings.