User blog:Planterobloon/Noob question about the FGH

How do people approximate numbers with it? At lower levels, it's pretty easy (I get why w+1(64) is comparable to Graham's number, for example), but right around 2w+x it feels like you can't possibly picture how the calculations would work. How would you know if a number was equal to, say, w^w^w(16), let alone the higher ordinals? Is it just extrapolating from smaller numbers in the same notation, or is it something else?