I don't know how new you are at this, but I thought I'd bring it up just in case since you are talking about limits. Be sure to read up on the SEC's rules for pattern day trading. You are allowed only 3 day trades in 5 business days if you've got less than $25,000 in the account.
http://en.wikipedia.org/wiki/Pattern_day_trader
I bring this up because you can easily find yourself in a position where you start buying groups of shares in the same company throughout the day and then you've got a limit that automatically triggers that same day. This does not count as one trade. If you bought groups of shares 5 different times that day and sell the same day, that is actually 5 trades and you must meet the SEC's special requirements of a pattern day trader or you risk being suspended for 3 months.