Just so happens I googled a question about head pressure this weekend and came across this site. Then today in class my instructor showed the class this site. Looks interesting and useful considering I'm a full time hvac student.
Decided to pursue hvac as my 2nd, permanent carreer after alot of research, and work/life experience. I always seem to get really involved in my work, and like a challenge and believe hvac is my calling in life.