  This note deals with stiffness tensors measured from anisotropic linear
elastic materials, whose symmetry is unknown. Their possible symmetries (exact
or approximative) are revealed by a pole figure. An intrinsic function allows
one to obtain a stiffness tensor which posses the chosen symmetry, the nearest
from the measured tensor, and its associated natural symmetry basis. For each
symmetry level, a distance between these tensors is given. The measurement of
the stiffness tensor is done with an ultrasonic direct contact method. It is
applied onto a 26 faces oak specimen.
