 This time, we're going to be looking at clock signals. A clock signal is a really, really simple waveform, but these are going to allow us to build nice resilient memory structures. So first of all, we can talk about one clock period, but there are several parts inside our clock period. We have a rising edge, a falling edge. We have some part where our clock signal is high and another part where our clock signal is low. This diagram is just showing the voltage over time. Start over here on the left-hand side, and our signal just goes up and down as time progresses. This is a nice idealization of our clock signal. We'd like our clock signal to look like this, where it's a nice square wave. We've got very, very sharp corners, but in reality it doesn't quite work that way. We construct these using a series of sine waves, so we tend to have a little bit of noise around our corners. But the results are still reasonably close to a square wave. Our memory units are going to take advantage of our clock signal to do certain things during certain periods of the clock. So we'll have some things that we'll do when our clock signal is high, but there will be other things that we'll only do when our clock signal is low. So overall, our clock signal is this nice, simple square wave that just repeats that a consistent frequency has a nice separation between high and low, so we can use this to keep track of when we want to do certain things.