Each weekday, TheStreet.com Ratings updates its ratings on the stocks we cover. Our model projects a stock's total return potential over a 12-month period including both price appreciation and dividends. Our buy, hold or sell ratings designate how we expect these stocks to perform against a general benchmark of the equities market and interest rates.While our 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 forecasted company earnings. Objective elements include volatility of past operating revenue, financial strength and company cash flows. Some recent rating changes are highlighted below. SYS Technologies ( SYS) has been downgraded to a sell from a hold. The company creates information connectivity systems for government and commercial clients, allowing them to monitor data in real time. SYS has reported a trend of declining earnings per share over the past two years. The company also posted a negative return on equity in the second quarter of fiscal 2007, which TheStreet.com Ratings feels is a signal of major weakness. The company had been rated a hold since May 2006. Private mortgage insurance provider Triad Guaranty ( TGIC) has been downgraded to a hold from a buy. Triad's revenue rose by just 27.9% in the fourth quarter of fiscal 2006 compared to the same quarter a year ago. Revenue throughout the thrift and mortgage finance industry grew at an average pace almost twice that rate over the same time period. TheStreet.com Ratings feels rising interest rates, mortgage loan reductions and a possible increase in delinquencies make stocks in this sector vulnerable going forward. Triad had been rated a buy since March 2006.