The notion of conformance provides a rigorous basis for testing
systems. In particular, a notion of hybrid conformance is useful in
establishing a formal model-based technique for cyber-physical
systems. A logical characterisation of conformance precisely specifies
the set of formulae that are preserved and reflected by conformance.
We present what is to our knowledge, the first characterisation result
for an approximate notion of hybrid conformance. To this end, we show
that the relaxation scheme used for preservation results in this
setting is not tight enough for providing a characterisation and
propose a tighter relaxation that we subsequently prove to be the
right one for characterising hybrid conformance.