 I've seen them on the shelf there from time to time, and what it'll do is it'll tell you if there is a presence of petroleum in the fuel. In other words, take a fuel sample, all right? Okay. And if there is, that's affecting how the DEF system is working. Keep in mind, it's a good first test, and it's a good maintenance test if you're changing filters on this yourself to keep these test strips around, because if you ever see signs of petroleum...