Generalizing a result of A.~Heppes we obtain the following characterization theorem: a convex body in a Minkowski plane (i.e., in a real two-dimensional Banach space) is of constant Minkowskian width if and only if every chord of it splits the body into two compact sets so that one of them has diameter equal to the length of this chord. In addition, we give a suitable extension of the ``only if'' part of this theorem to higher dimensional Minkowski spaces.
Keywords:
body of constant (Minkowskian) width, diameter, section, hyperplane, Minkowski space