Going thru the last part, the part on forms (the book is HUGE), in the fifth edition. Wonderful exposition, every other resource I've consulted on the subject has done little, if anything, to demystify the concrete nature of forms. More importantly, it has the best exposition on exterior calculus (apart maybe from Needham's Visual Differential Geometry). Many texts define the exterior derivative thru its rather opaque properties (especially opaque is the so-called antiderivation property, and the Poincaré lemma). Moreover, even if they satisfied the properties of the more familiar Newtonian derivative (of 0-forms), it wouldn't be entirely clear that satisfying these properties uniquely identifies a map capable of doing differentiation. Haven't gone through the vector calculus and linear algebra parts but given the exposition in the last part it's clear that they too would be chock-full of insights.