OJT, I started out as a burgler alarm installer. Way back in '75. Had a fight with a boss and went to work for an electrical contractor. (EC). Worked for him for 8 years took the test and got my own EC's lic. satyed with the boss for at least a year. Worked on the side ( 7 days a week) then finally parted company with the old boss. ( still friends) Went into my own business for 15 years then became an AHJ. I believe that the better AHJ's have had field experience and not just book smarts.