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 truck maker Navistar International (NYSE: NAV) fell 10% today after the company updated guidance for the fiscal third quarter.

So what: The company said that fiscal-third-quarter revenue would likely be $2.8 billion to $3.0 billion and the company would have a pre-tax loss of $105 million to $145 million. The problem is that analysts had expected revenue of $3.5 billion and a profit of $0.09 per share.

Now what: Navistar has missed estimates by a wide margin in the last two quarter and, despite rapidly falling estimates, will likely miss again this quarter. The company is accelerating delivery of ICT+, the company's next-generation engine, but it seems to be having a negative impact on current results. Until the company's strategy change is proven, I see no reason to buy the stock, so I'll sit out the discount today.

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Fool contributor Travis Hoium does not have a position in any company mentioned. You can follow Travis on Twitter at @FlushDrawFool, check out his personal stock holdings or follow his CAPS picks at TMFFlushDraw.

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