Merriman specializes in market-timing services, and his collaborator is a securities broker turned financial writer. While their guide affords an accessible introduction to market timing, it vastly overstates the case for this approach to equity investing. In brief, timers try to shift portfolio assets between common stocks and income-yielding commitments in response to or anticipation of major market moves. Any number of indicators based on technical, fundamental, and other factors (including psychology) may provide the cues for their buy, sell, or hold decisions. Merriman's system focuses on when equity investments should be made rather than on specific issues to buy; consequently, he favors the use of commission-free mutual fund groups that permit no-cost (or low-cost) switching. As a practical matter, the authors' promise of annual returns averaging 20 percent is apt to prove elusive on several counts. For one thing, it's all too easy for do-it-yourselfers(and pros) to misread signals, even those flashed by the relatively simple three-element series the authors prefer. For another, market timing, while far from a mainstream discipline, has caught on to the point where concerted action by adherents is liable to swamp certain funds with redemptions or flood them with new cash, thereby skewing their performance. Formulaic schemes designed to take the guesswork out of timing are only as good as the capacity of their indicators to detect significant turning points. In accentuating the positive aspects of market-timing techniques, Merriman and Dowd scant the downside dangers that may result from untutored application. Their text, which includes charts, tabular material, and up-to-date directories, has modest appeal for Wall Street veterans seeking the latest slants on a trendy thesis, but it should be labeled potentially hazardous to the fiscal health of rookies.