 Nothing illustrates engineering design better than a mobile phone. In fact, a definition of engineering might be something like design with real world constraints. Here's the seven major constraints that govern the choices made by an engineer in designing a cell phone. The essential trade-off in any cell phone is compactness versus usability. We want a small phone but also one that fits our bodies. Here's three solutions. A hinge, the classic flip phone. Put a hinge in and change the size and it allows you to have larger keys. You can also see the same idea in slider keyboards. Second, you could do what they do on this phone, a blackberry, and maximize available space by using very tiny keys. And you can use software. This is my Android, the phone I use every day and I've added to it a clever little keyboard designed for small devices. I can spell my name just by doing this. Very clever, isn't it? Next, emotions affect the design of a cell phone. You don't see these too much today but the flip of this now nearly vintage phone resonates deeply in the psyche of someone my age. I grew up watching Captain Kirk grab his communicator and bark a command, beam me up Scotty. I'm sure phones today resonate in some way with video games or popular movies. Now, next, in making a compact design, an engineer considers energy. In the 20 years or so that I've been using a cell phone, they've shrunk. Hold on. Look at how huge this vintage brick phone is from the 1980s. This isn't even one of the first ones. It's one of the later ones called an ultra classic two, slightly smaller than the first phones. It weighs just over a pound and it seems to be mostly battery. It uses a nickel cadmium one compared to this lithium ion battery from a more modern phone. Now batteries shrunk because they got better. We have greater energy density now. But likely more important is the move from analog to digital signaling and a movement of much energy draining computation from the phones themselves to the towers. The next constraint also helped reduce battery size. Old cell phones had rick sized batteries, partly because it took a lot of power to reach a cell phone tower. But today we have such a density of towers that we don't need as much energy to reach one. The increase in towers has made this a nearly endangered species. For this razor, this is the closest indication of an antenna. It's a rubber cover for the external antenna connector used during testing of the phone at the factory. The actual antenna is inside, underneath one of the plastic parts of the case of the phone. Now this doesn't work as well as a huge external one, but that's the trade-off between compactness and usability I mentioned earlier. Now another reason for a phone's compactness is plastics. If we didn't have plastics, this phone would be much larger and more expensive. Just take this latch. Imagine how bulky some kind of clasp would be, the fact that this plastic gives a little bit and pops back into place makes this simple, small fastener possible. The phone's designer needed a deep knowledge about how plastic behaves so it could be used thousands of times without wearing out. The insides, the way a phone operates, reflects yet a sixth design criteria. On most modern cell phones, you'll find something called Enhanced or E911. In an emergency, an operator can locate the phone within several hundred feet. Typically it doesn't use true global positioning, but instead assisted GPS in that it uses the location of cell phone towers to triangulate. Now this is fraught, of course, with all types of privacy issues. Lastly, we need this phone to quickly change the volume because it's a culture. We've decided that there are times when our cell phone shouldn't ring, and so we can adjust the ring tone volume easily. I'm Bill Hammack, the engineer guy. Hi, how did you get this number?