Be warned that Fidelity has been providing incorrect data for NYSE TICK for the last two months. I have been trying to have them correct the data but so far have had no success. 1-minute tick data should range between negative 1200 and positive 1200. Fidelity's data ranges between zero and positive 1200. All negative data points in Fidelity's historic data have been replaced by zeros. Their real-time data is correct. The NYSE tick is commonly used as a short term trading indicator. The NYSE tick represents the number of stocks ticking up minus the number of stocks ticking down on the NYSE. If the Tick reads positive 500, for example, then there are 500 more stocks on the NYSE ticking up than there are ticking down. Conversely if the Tick should read negative 500, this means 500 more stocks are ticking down than are ticking up.