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: After today's 7% drop, Investors in natural gas engine tech expert Westport Innovations (WPRT 0.87%) have been hammered down 58% during the past six weeks. The falling stock price is a product of bad business results, and greater macro fears. On September 30, Westport revised its guidance for the full year down a whopping 25%, and stated that it would fall short of its goal of adjusted EBITDA-positive results for its three operating segments. Management cited Europe -- its biggest market for its core business -- remained soft, along with Russia and China, as well as delays in its co-development agreements with heavy-duty truck and engine makers to bring its high-pressure, direct-injection, or HPDI, technology to the market. 

Furthermore, the price of oil has fallen as much as 20% since June on increased supply and relatively flat demand. This matters for Westport because one of the primary drivers of natural gas engines is the cost-savings of NG versus both gasoline and diesel. 

So what: Unlike natural gas refueling leader Clean Energy Fuels (CLNE 4.26%), which has seen its stock fall more than 40% during the same time, the news is certainly material to Westport Innovations, and it largely "earned" the pummeling the market has given it. However, it's important to separate what's material from what isn't. Let's start with oil prices.

The cost differential between gas and diesel and natural gas is the primary driver behind sales of NGVs, and the falling price of oil can spook the market pretty quickly. However, oil would have to fall much farther to have a serious impact on the cost advantage of natural gas. However, softness in Westport's biggest markets, and delays in HPDI -- which is supposed to be a big driver for growth -- is clearly material. 

However, there are a couple of bright spots out there. First, sales of Westport's 12 liter ISX12 G, being co-built with Cummins (CMI 0.36%), are on track to meet targets for 2014 according to a number of industry experts. Sales of natural gas trucks in 2014 are expected to have grown 27% this year versus 2013. Also, part of the delay in bringing HPDI to market is Westport's shift to HPDI 2.0, and the adoption of HPDI 2.0 by development partners like AB Volvo (NASDAQOTH: VOLVY). The injector components are expected to be manufactured in Westport's venture with Delphi Automotive (DLPH), and the costs will be less than earlier versions, helping natural gas engines be more cost-competitive with diesel. 

Now what: This is yet another in a series of delayed results from Westport, and I can't fault investors who decide to move on. However, It's worth acknowledging that the heavy trucking market that HPDI is targeted at is historically very slow to adopt change. When you consider that each truck costs more than $100,000 -- and that the NG version can add an extra $50K  -- and that the refueling infrastructure has been slow to roll out in many areas, it's understandable that truck and engine makers aren't rushing to build engines before they know there will be demand.

Another year, another delay from Westport. I intend to hold -- largely because Westport's technology is still valuable as demonstrated by its partnerships; but also because there has been pretty decent growth so far from the ISX12 G. This is evidence that -- eventually -- natural gas engine adoption will ramp up in heavy trucking, even if the industry is moving at a glacial pace right now.

Furthermore, management has cut operational expense in recent quarters, and the company's capital position is probably sufficient for another year or maybe two. That should be enough time for adoption to start ramping up, and Westport to be closer to profitability. If you're tired of waiting, I understand. It's still going to take time for the story to play out.