 So if you have a pipe with two closed ends, you'll tend to get this kind of thing, and if you have a pipe with two open ends, you tend to get that kind of thing. And finally, of course, all of these are just the fundamentals. You can also get higher harmonics. For example, for closed, closed, you could have this kind of shape, or for open-open, you could have this kind of shape, or ones with more wiggles in until you get the right combination of nodes or anti-nodes at the ends. So there's a whole set of higher harmonics that apply to any particular situation, open-closed, closed-closed, or open-open. And if both ends are open or both ends are closed, then the length is related to the wavelength in the following way, where n is one, two, three, and so forth. And if you have this case where you have one open and one closed, then that lowest one is lambda on four, the length is lambda on four. Then the next one, you're going to have an extra half-wavelength, so that'll be three lambda on four, five lambda on four, and so forth. And so a formula that gets all of that is, again, for n being one, two, three, and so forth.