The xkcd geohash algorithm relies on the most recent Dow Jones Industrial Average OPENING value. This is potentially dangerous. The opening value is a result of overnight trading when there are relatively few buyers and sellers, so a single small investor might be able to deliberately affect the opening price by a penny (especially when the average falls very close to a 0.005 rounding region), providing a tiny bit of control of where the location will be, perhaps for nefarious purposes.
Better would be the most recent Dow CLOSING value. Those trades take place during the day, when no single investor has much control. There are probably many last-second trades which would thwart anyone trying to control the closing value down to the penny.
Use the closing value of some other major stock exchange index if you want a more convenient daytime value in North America. Tokyo (Nikkei) closes at 1 AM Eastern, London (FTSE) at 11:30 AM Eastern, India (SENSEX) at 5 AM Eastern.
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