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Figure 6 shows us another part of our PRESTO plot &mdash we still have phase on the x-axis, and the darker bins still mean that we detected a stronger signal. However, time on the y-axis has been replaced with frequency, or sub-band. We already talked about spin frequency, which is how many times a pulsar goes around in one second. In the current plot, though, we are actually talking about our observing frequency. This is the frequency of the radio waves that we are actually collecting with our telescope. You may notice that the frequency is measured in megahertz (MHz). Your car radio typically picks up signals with a frequency of 88 &ndash 107 MHz (the FM band). It is important to realize that this is different than the spin frequency (which is usually no higher than a few hundred hertz). Now, you will notice that in addition to being labeled with "Frequency (MHz)", the y-axis is also labeled as "Sub-band". The instruments we use to collect and measure our radio signals actually break down the signal into small chunks of observing frequency. Each one of these chunks is called a sub-band. It is typical for us to use 32 or 64 sub-bands, and if you look closely, you should see that this in fact the number of sub-bands on the plot. Each gray bin in this image represents the power collected in a single sub-band over the full observation. You can also think about it as the power collected in some small chunk of our observing frequency. If you look closely, you should see an increase in signal strength, which appears as a dark line on our plot. You should see it at the same phase in both the time series and frequency/sub-band plots. Examining the characteristics of this signal helps us to determine if we are looking at a real pulsar or some source of RFI (we will talk about that later on).