  We revisit the transformation rules of the metric and Kalb-Ramond field under
T-duality, and express the corresponding relations in terms of the metric G and
the field strength H=dB. In the course of the derivation, we find an
explanation for potential reductions of the isometry group in the dual
background.
  The formalism employed in this paper is illustrated with examples based on
tori and spheres, where for the latter we construct a new non-geometric
background.
