Normally, I don’t follow the stock market, and I follow the imperfect Dow Jones Industrial Market even less, but over the space of what looks to be about ½ an hour, the Dow fell 600 points, and then rose by 400 points.

In percentage terms, that’s about 5½% down and about 4% up in a very short time frame.

I’m wondering if the whiz kids with the high frequency trading robots just screwed the pooch somehow.

(Update)

We now have a potential cause, sloppiness and lack of controls:

In one of the most dizzying half-hours in stock market history, the Dow plunged nearly 1,000 points before paring those losses in what possibly could have been a trader error.

According to multiple sources, a trader entered a “b” for billion instead of an “m” for million in a trade possibly involving Procter & Gamble , a component in the Dow. (CNBC’s Jim Cramer noted suspicious price movement in P&G stock on air during the height of the market selloff. Watch.)

Sources tell CNBC the firm in question that handled the erroneous trade is Citigroup . The bank said it has no evidence of a bad trade but is investigating the situation

We now have some hard numbers:

Here is the time frame, courtesy Scott (from MarketWatch):

2:38 PM: Dow down 360

2:48 PM: Dow down 600

2:51 PM: Dow down 900

Dow is now down around 500 [around 3:40 pm]

Whatever is going on here, it appears that Bloomberg News Service got absolutely hammered, and is now (about 4:30 pm) inaccessible.