Thanks Dynamite, Framer, Ozlander1, JeroenC. My quest to learn about differential pressure control, as led to me learn about various other types of pressure controllers used on other aircrafts.
After asking the same posted question on pressurisation to various pilots / techs , I have always got a different answer.
The Boeing FCOMs, are good but written on a need to know basis.
Dynamite when you say it saves cost? You mean for the airframe or the controller it self?
By the way when I used the term "Push Button Pilot", its a term used to describe pilots, who fly modern flight decks, and actually push buttons to fly the a/c. You will need to be in the industry long enough to know about it. Most people don't want to know why?
Thanks a lot people.