The 8/22 day EMA crossover indicator is used to trigger short term buy and sell signals.  When the 8 day EMA (blue line) crosses above the 22 day EMA (thick black line), it triggers a buy signal, and when the 8 day EMA crosses below the 22 day EMA, it triggers a sell signal.  As we can see from the chart below, the 8/22 day EMA does a good job of getting & keeping a trader long in an UP trending market, and getting & keeping a trader short (or out) in a DOWN trending market with relatively few whipsaw/false signals.