Why is land close to the Wall Street Stock Exchange so expensive? Because being 100 feet closer to the exchange's switch means your computer can make micro-transactions faster, translating into millions of dollars in high-frequency trades. Those trades apparently caused havoc on the market again today, in one 10-minute stretch knocking the index down nearly 700 points and 900 at one point on the day, erasing over $1 trillion in equity values. NASDAQ and the NYSE are apparently canceling trades executed in that time frame pending an investigation.