The TICK updates continuously through the session and typically oscillates within a few hundred either side of zero. Readings beyond plus or minus 1000 indicate a large number of stocks moving in the same direction at the same moment.
Intraday traders use extremes as short-term exhaustion markers, and use the distribution of readings through the day to characterise the session: a day that repeatedly prints high positive TICK and never goes deeply negative is a trend day.
It is extremely noisy and easy to over-interpret bar by bar. It also reflects only NYSE-listed issues, which is a shrinking and unrepresentative slice of the market, and its typical range has shifted over the years so historical thresholds need care.
Related: trin, market-breadth, relative-volume, initial-balance, volume-climax