For instance, to form a proto-vrddhi derivative from *dyew- 'sky' one took the zero grade *diw-, inserted *e to give *deyw- (sic), and so derived *deyw-ó-s 'god' (literally 'skyling'). . . . This is the historical source of the derivational process called vrddhi in Sanskrit.
—Don Ringe, From Proto-Indo-European to Proto-Germanic. The book actually uses the Indo-Europeanist syllabicity ring under the r, but I can't find that in Unicode.