Abstract. To each function f of bounded quadratic variation we associate a Hausdorff measure μ f . We show that the map f → μ f is locally Lipschitz and onto the positive cone of M[0, 1]. We use the measures {μ f : f ∈ V 2 } to determine the structure of the subspaces of V 0 2 which either contain c 0 or the square stopping time space S 2 .