These alerts are a subset of their unfiltered counterparts.  When the price quickly changes several times in a row, only one of these alerts will appear.  The unfiltered alerts appear once every time the price changes.

Typically no more than one alert per stock will appear each minute.  However, if a stock price changes by more basis points than expected, new alerts will be displayed more often.  The cutoff point for each symbol is automatically chosen based on volatility.

Daytraders often prefer to display the unfiltered versions of these alerts on a large set of stocks.  The effect is to create a window where the user can quickly see if the market as a whole is moving up or down.  Other traders prefer to see fewer, more interesting alerts.  For that effect, select these filtered versions of the alerts.  Some people create two or more alert windows, some with filtered alerts and some with unfiltered alerts.