Usually there are fairly big swings in the NYSE TICK index, with values between 1000 and -1000. For some reason, yesterday had abnormally small swings, with the TICK never reaching values above 500 or -500! Was some parts of the markets closed or why were the values so low yesterday july 27? The attached graph shows the TICK during the last two days, as you can see the difference between fridays and mondays TICK range is huge. It does not look normal, hence my question.