$40 is not starting salary! In VT it takes 5 yrs to be a master plumber. And guess what, you'll likely start at $12! After 5 years, if you pass the test, you're still no where near $40, if you work for someone else.

My comment was that the engineering salaries are starting salaries. What is being compared is an established plumber's salary versus a starting engineering salary - an invalid comparison.