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 3D Systems (NYSE:DDD) were down by as much as 10.9% this morning after rival Stratasys (NASDAQ:SSYS) released its second-quarter results before the market opened today.

Why It's Happening: In the second quarter, Stratasys' revenue increased by about 2% year over year to $182.3 million, translating to a net loss of $0.55 per share, or an adjusted net profit of $0.15 per share. These results fell in line with Wall Street expectations calling for Stratasys to generate $182 million in revenue and earn $0.15 per share in adjusted earnings.

The market doesn't seem to have taken kindly to the fact that Stratasys withdrew its full-year guidance, but provided guidance for the third quarter, which fell significantly below analyst expectations.

In the third quarter, Stratasys anticipates to generate between $175 million and $190 million in revenue and earn between $0.03 and $0.13 per share on an adjusted basis, whereas Wall Street was hoping it would generate $216.5 million and earn an adjusted $0.47 per share.

As far as 3D Systems is concerned, the 3D printing company is slated to report its second-quarter earnings on Thursday, August 6. At the time of this writing, Wall Street expects 3D Systems to grow its sales by nearly 15% year over year to $173.7 million and take home $0.09 per share in adjusted earnings.

It seems this is a classic sympathy sell off, where 3D Systems investors are reacting negatively to a downbeat development from a competitor. Fortunately, investors won't have to wait long to find out if today's action was warranted.