You've got it right. At the bottom of the project's website[1] is a list of publications of which two explain it well - and they're available as free .pdf's:

1. http://scholar.google.com/scholar?q=%E2%80%9CPassive+exoskel...

2. http://scholar.google.com/scholar?q=A+Simple+Technique+to+Pa...

[1]: http://www.nemours.org/research/labcenter/orthopedics/perl/w...