What you are looking at is relative PPP, which claims that exchange rate movements are explained by relative inflation movements, see wiki. However from the picture I would guess he is looking at a bottom up purchasing power parity aggregate, which as @user1483 eluded to, is a different calculation. There are several providers of this type of index, the OECD provides one. A brief description of their methodology is explained here and a more detailed description can be found here. Ultimately the two are related and under a set of set of economic assumptions on the world (which don't hold empirically) are equivalent however practically speaking the calculation methodologies are quite different and will yield different results.