  We study structurable algebras of skew-dimension one. We present two
different equivalent constructions for such algebras: one in terms of
non-linear isotopies of cubic norm structures, and one in terms of hermitian
cubic norm structures.
  After this work was essentially finished, we became aware of the fact that
both descriptions already occur in (somewhat hidden places in) the literature.
Nevertheless, we prove some facts that had not been noticed before:
  (1) We show that every form of a matrix structurable algebra can be described
by our constructions;
  (2) We give explicit formulas for the norm $\nu$;
  (3) We make a precise connection with the Cayley-Dickson process for
structurable algebras.
