  An experimental set up, dedicated to isolate an error present in the
$\eta$-algorithm, gave an unexpected result. The average of a center of gravity
algorithm at orthogonal particle incidence turns out to be non zero. This non
zero average signals an asymmetry in the response function of the strips, and
introduces a further parameter in the corrections: the shift of the strip
response center of gravity respect its geometrical position. A strategy to
extract this parameter from a standard data set is discussed. Some simulations
with various asymmetric response functions are explored for this test. The
method is able to detect easily the asymmetry parameters introduced in the
simulations. Its robustness is tested against angular rotations, and we see an
almost linear variation with the angle. This simple property is used to
simulate a determination of a Lorentz angle with and without the asymmetry of
the response function.
