I've been poking around more in multiple exchanges and ECNs, and am seeing the fairly large spread that can exist between them. I'll see roughly 12 exchanges or ECNs issuing quotes from the IQFeed. Does ThinkOrSwim source from the public exchanges and ECNs, and then just report in the last trade from whichever is more recent? Like if the last trade on Nasdaq for XYZ was 100.13, and 50 shared were sold on the Boston Stock Exchange for 100.10, would ThinkOrSwim display 100.10? Is it aggregating the activity from all exchanges, since it does "smart" routing on the execution side? I tried looking this up on ThinkOrSwim and found this link, which doesn't really answer the question as to how their quotes are structured.