For each Borel set of reals A, of finite rank, we obtain a "normal form" of A, by finding a Borel set Ω of maximum simplicity, such that A and Ω continuously reduce to each other. In more technical terms : we define simple Borel operations which are homomorphic to ordinal sum, to multiplication by a countable ordinal, and to ordinal exponentiation of base ω1, under the map which sends every Borel set A of finite rank to its Wadge degree.