I'll throw this out there: what if the clock in Chicago was just 5ms slower than the one in NYC. The logs would show the transactions happened at the same time,

I'll throw this out there: what if the clock in Chicago was just 5ms slower than the one in NYC. The logs would show the transactions happened at the same time, but they didn't. The NYSE mandates that business clocks never drift more than 1s from the atomic clock [1]. What is the resolution guaranteed between the two clocks being compared? After all, it's impossible to guarantee perfect synchronization of two clocks at any distance (bounded by the speed of light and the drift rate of the clocks) [2]. The only retort I can think of is why do the other players react at the proper time. [1] http://www.nyse.com/nysenotices/nyse/rule-changes/detail;jsessionid=32D8706B7E53902582A32376B5F50B09?memo_id=12-1 http://www.nyse.com/nysenotices/nyse/rule-changes/detail;jse... [2] Cristian, F. (1989), "Probabilistic clock synchronization", Distributed Computing (Springer) 3 (3): 146–158