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's happening: Shares of construction company MasTec (NYSE:MTZ) dropped as much as 17% today after it announced first-quarter results.

Why it's happening: Revenue grew 4% from a year ago to $1.0 billion, and the company lost $6.9 million, or $0.08 per share. On an adjusted basis, continuing operations generated earnings of $0.07 per share, which was still $0.11 below estimates.  

The first-quarter results were a little disappointing, but second-quarter guidance was even worse. Management said it expects revenue of $1.0 billion and earnings of $0.27 to $0.30 per share, while Wall Street's estimate was for $1.12 billion in revenue and $0.37 in earnings per share. Full-year earnings are expected to be $1.45 per share, well below the $1.76 analysts expected.

Management blamed bad weather and a weak Canadian currency for some of the weak results, and an audit committee investigation is adding costs as well, even delaying the 2014 full-year annual report. But it's also clear that momentum is slowing, as indicated by slow growth, and earnings are definitely headed lower near-term.

Shares are also fairly expensive for a construction company at 11.5 times 2015 guidance, and I'd like to see revenue and profits head higher -- and learn the results of the audit committee investigation -- before thinking shares are ready to recover.