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 IPG Photonics Corporation (NASDAQ:IPGP) finished the trading day on Tuesday with close to a 6% loss after dropping to a 10% loss early in the morning. Investors seem unhappy with the fact that IPG's upcoming quarter is looking a little soft, despite the fact that the company bested top-line expectations for its fiscal first quarter.

So what: IPG's first-quarter revenue came in at $170.6 million, a 20% year-over-year improvement that also cleared analyst expectations of $168.1 million in revenue. The company's bottom line showed $0.77 in earnings per share, which matched analyst expectations. Looking ahead, IPG now expects to generate between $173 million and $188 million in revenue for the second quarter, which will result in a range of $0.77-$0.92 in EPS. Analysts had modeled a second quarter with $187.1 million in revenue and $0.90 in EPS, so the midpoints of IPG's guidance -- $180.2 million in revenue and $0.85 in EPS -- fall beneath those estimates on both counts.

Now what: It's hard to call this bad guidance, as it IPG's midpoints would represent year-over-year growth of 7% on the top line and 6% on the bottom line. However, this is not particularly strong growth for a company that just posted a year-over-year growth rate of 20% in revenue and 15% in EPS. Slowing growth is always a concern, particularly for a company that's seen its share prices rise primarily on P/E expansion over the past year. Tread cautiously with IPG. It's not a screaming buy today, but it's hardly in the nosebleed-P/E territory it once occupied, either.