It's a hypothesis made for the application of the "lambda-tracking" method of control : the system must have a relative degree one !..i don't have much more details on this hypothesis.
[ lambda-tracking is a relatively recent controller design method (adaptive control) ]
Dahlia, I do believe it is form of terminology derived from Statistical Process Control methods. As for it's exact meaning you"ll need to get involved in the intricacies of the method. Do a Google seaarch on the term "relative degree one". You'll come up with about 2 mil. hits.
this control mechanism is extensively studied at the german university of stuttgart. use the link below to go to the according r&d-website. the second link is the direct link to the publications made in this context at stuttgart university.
