Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of rural telecom Atlantic Tele-Network (Nasdaq: ATNI) plunged as much as 19% over the weekend, but have traded just 3% below Friday's closing price all day long. The trading volume is anemic as always, with only 11,000 shares changing hands today.

So what: That low-volume action is actually the reason for the drop. Atlantic generally trades in small batches; looking at a current order book, it would take no more than a sell order for 376 shares right now to eat through bids all the way down to $30.95 per share. That would set the stage for a 20% drop on the next sell order.

Now what: Look, touching low-volume stocks always, always requires limit orders. Taking whatever market price you can get may be convenient, but can bite you every now and then as it did to some poor sop in this case. Atlantic peer Cincinnati Bell (NYSE: CBB) suffers from the same tiny-volume malaise, while other sector rivals such as Alaska Communications Systems (Nasdaq: ALSK) and rural-telecom giant CenturyLink (NYSE: CTL) do not. I'd suggest getting into the habit of placing limit orders either way, because you just never know when or where the system will foul up again.

Flash crash, anyone?

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