Because of this limitation, we instituted a login procedure
for all of our example applications. Specifically, when a
user wants to join a multi-user collocated interaction, he
must first press and hold a “login button” (see Video Figure).
This triggers the system to capture an impedance profile
(of the finger pressing the button) and retrain the classifier.
As discussed in the evaluation section, this interaction
can be completed as quickly as 500ms.