Thanks very much for the considered reply Cabbie. I prefer to be more conservative, indeed be backed also by a DVI crossover (either before or after the MACD cross). But either crossover type, in the positive or negative zone, puts a stock on my watchlist. Concomitantly, downcrosses on either MACD or DVI are viewed as a sell signal.
Sure, wrong plenty of times; and never pick a bottom with these criteria (although took a punt on on SLR when it put in a longterm low on its Bollinger Band Width - very often indicative of a sharp move, up or down). But it seems to work better for me than crossovers in the negative zone.