When it comes to MACD…12,26,9 is the stock and most widely used setting. Often stock settings have the most eyes and are the most valuable when it comes to indicators. In my example…12 is the slow EMA, 26 is the longer EMA and 9 is the smoothing line. The moving lines you see on plotted MACD are 12 (slow EMA) and 9 (smoothing line), the 0 horizontal level represents the 26 (longer EMA). In the background on MACD you’ll often see a histogram, this measures the difference between the slow EMA and smoothing lines and plots this data in an easy way to watch momentum change incrementally. Both pieces of MACD are useful for spotting momentum shifts and divergence.

With 3 lines of interest plotted you can have 2 major crossovers.
1)Slow EMA crossing the fast EMA (0 line) (red circle & arrows)
2)Slow EMA crossing the smoothing line (black circles & arrows)

Most use the slow EMA crossing the smoothing line as indication of a momentum change. Sometimes on longer time frames like the above weekly there is no divergence needed for a mid term reversal and when slow and smoothing cross its a big move. See the below link for an article I wrote on divergence.

http://www.tradersbase.com/forum/technical-analysis/469-whats-divergence-diverging-indicators.html

Note: The most recent down move has built bullish divergence (green lines) where price tested lows yet the MACD as well as the MACD histogram failed to even come close to their prior lows. This was a VERY bullish indicator. I would have preferred the volume had been lower on the 2nd test giving a 2nd and more important diverging indication though. That would have told me there were less sellers at a prior key level and we didn’t get that so I’m not a total believer of this rally yet. I will become more bullish if/when the same level (or lower) has very low volume aka: brings out very few sellers. I will become full bull when the red downtrend and structure resistance are cleared and legitimately defeated.