Persistence of identification: Calibration seems to be sensitive
to changes in the human body over the course of the
day. Thus, walking away and returning hours (or certainly
days) later is not currently possible. We hypothesize that
environmental factors, such as ambient temperature and
humidity, as well as biological factors, such as blood pressure
and hydration, cause impedance profiles to drift over
time. This personal change variability can be larger than
between-person variability. This suggests use scenarios
where interaction is ad hoc and relatively short, or where
the precision of recognition is not critical.