I was kind of worried about what the "essential Triangle tool" was (never bothered looking) and here all it is - is the Easy Triangle and Companion Triangle combined into one. Since I bought them for last year's mystery, I can use them if I want. I love using those two rulers and have been using them a lot with the 365 block challenge, since I don't like all the waste using the covered corner method, and I couldn't get the hang of the "fast flying geese".