If you have level 2 watch it side by side with your traders platform time and sale ticker during the day on level 2 you will see trades with letters behind them. But they don't show up on my scottrade Time and Sale. And at the end of the day the volumes are different. So if you want to see to believe watch your level 2 with your traders time and sale and then decide. I see it all the time. Compare the letters with the list I posted.
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