Whenever people buy or sell stock, they must report the transaction to the exchange.  The exchange then forwards that report.  The report of a single transaction is called a print.  This is short for “print the tape.”  The print includes the time, the stock symbol, the average price, and the total number of shares.

A print is the smallest piece of data related to buying stock.  Our alerts server looks at each print for all stocks that we track.  Some alerts can be based on a single print; these are the fastest alerts, but they also have the most noise.  The alerts server also accumulates data about all prints for a stock and performs statistical analysis on that data.  This allows us to filter out the noise.