problem is the individual control required needed too : must it be mechanically activated by hand or can it be sensed?
Local control: Does the control need to be at the fitting/desk or could it be at some convenient nearby point to the fitting/desk?
It is what in systems engineering we used to call 'the irreducible minimum user (by whom, how, why, what, where, when, how well, in this/these environment(s) with these conditions and rules) requirements'....from which one then develops the system requirements and thence to the design implementation.