OTOH, and for example, reducing "user friendliness" to component metrics,
then designing to the metrics, can result in a system that's pretty darn
user hostile. I don't think that a few such guidelines in a functional
specification are off base, as long as they're delineated as such.
Control systems and communications consulting
Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott