 So how do we go from having some knowledge of the ongoing components in DNA and having these X-ray based scattering plots and using that to determine a good model, a structure of DNA? Well, Watson and Crick kind of borrowed, well they didn't borrow their access to Maurice Wilkinson, Rosalind Franklin's scattering curves. But their great contribution here was that they were not the ones doing the experiments, but they thought deep and hard about the experiment. And they used one more observation that had been published a few years earlier by Erwin Schargaff. So Erwin Schargaff had published a paper where we had noticed that these bases appeared to be pairwise somehow similar, that the number or the concentration of adenine tends to pretty much always equal the number of timings and similarly the number of guanine bases always equals the number of cytosine bases in a particular cell. If you go to a different organism or something it might be slightly different, but pairwise they always appear to match up. Which again, when Erwin Schargaff published it was an interesting observation, but the reason for this wasn't known. And then on the other hand we had this strange model by Pauling and Corey that had the triple helix. In this model there is no particular reason why they should pair up, right? And then we had these molecules that we somehow want to understand why do these nucleotides if we have the full one pair up. So what Watson and Crick did is that they realized that that pairing is going to work great if you had a model where bases bind pairwise to each other. And if bases are going to bind pairwise to each other they need to face each other, right? And that would require you to turn the phosphates outwards, which is pretty much how they came up with the idea of this double helix. It's one of those things that in hindsight it turns out to be obvious, but it wasn't so obvious. Even Linus Pauling is one of the most famous chemists of the 20th century who didn't have the idea. That also leads to that you have this very specific pairing of the bases in DNA, which is cool for another reason that I'm going to come back to. This stabilizes the entire structure, too, rather than having floppy bases pointing out if the bases are bound to each other using hydrogen bonds. And those phosphates are solubilized and stabilized by ions because they're charged. It's going to create a very nice long-term stable structure, which is good in general. At the time, there were no strong computers, so the way Watson and Crick it's easier to have the idea, right? But to prove that your idea is right, you then have to build models and then they had to use a ruler and measure the distances between all the heavy atoms and manually calculate these diffraction spectra and prove that if this model were to be put inside a synchrotomor X-ray, it's going to be a lot easier to and prove that if this model were to be put inside a synchrotomor X-ray beam at the time, you would indeed generate a diffraction pattern that corresponded to the one measured experimentally by Rosalind Franklin and Maurice Wilkins.