Hi @Karim_B That's because the prior version of Gregory's text contained this topic in Chapter 7, but the current version points to Chapter 12; i.e., the topic moved chapters between versions. @Nicole Seaman will confirm on Monday when she returns ... FYI, I can see in our internal project manager that I am soon going to be re-recording these Gregory chapters, hopefully can wait just a little while. We have improved slides and exhibits coming for the Gregory topics (actually, informed by Gregory's 3rd edition, now that we can see GARP will be retaining this in 2018). Sorry if that's confusing (there are actually three editions of Greogry) but the bottom line is (i) the chapter 7/12 isn't actually a "problem" because the topics just moved chapters but (ii) we also have new videos coming soon on this. Thank you!