These alerts appear when the stock price moves very quickly.  The exact number of basis points required to set off this alert depends on the volatility of the underlying security.  To assist daytraders, this alert works on a time scale of approximately one minute.  Bad prints are filtered out, and will not cause this alert to appear.

The description of each alert includes the size of the move.  Roughly speaking, this number shows how much the price has changed in the last minute.  However, the alert will be reported as soon as the underlying security meets the minimum criteria, which may take less than one minute.  Often the price continues to run in the same direction, so the final size will be larger than the size reported.

This alert will only be reported when the price makes a clear, statistically validated move in one direction.  It will not be reported every time the price of the last print moves by the price displayed on the screen.  Otherwise, random noise would cause this alert to be reported more often.

More options related to these alerts are listed below.