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 Core Laboratories (CLB) plunged 18% today after the energy services provider lowered its current-quarter and full-year guidance.

So what: The stock pulled back sharply in April on disappointing first-quarter results, and today's second-quarter guidance cut -- $1.32-$1.35 in earnings per share on revenue of $265 million-$270 million versus its prior view for $1.48-$1.53 and $280 million-$286 million -- implies that the headwinds working against Core are only getting stronger. On the bright side, management said the warning is due to a drop in demand and not a loss in market share for targeted core analyses jobs, suggesting that Core's competitive position remains strong.  

Now what: Due to the weak current quarter, management now sees full-year EPS of $5.80 to $6 on revenue of $1.1 billion, down from its prior view of $6-$6.25 and $1.155 billion-$1.175 billion, respectively. "The lowered second quarter 2014 revenue and EPS guidance are primarily caused by North American clients that now project sampling and analyzing less than previously expected levels of reservoir fluids from established unconventional plays in the Marcellus, Bakken, Montney, [Niobrara] and Eagle Ford formations," wrote Core Labs. "A reduction in the number and length of cores cut and analyzed from these reservoirs also is causing the decrease in the Company's expected revenue and EPS in the second quarter of 2014." With the stock now now off about 30% from its 52-week high, however, those short-term concerns might be providing patient Fools with a high-quality long-term opportunity.