I am a retired engineer.
I began as an undergraduate physics major desiring to teach physics at the high school level. In my 3rd year I changed majors to engineering (to theoretically make more money). While working as an engineer my avocation as a side job was to teach review classes for the PE fundamentals exam (FE) in the subjects of electrical and computer engineering, thermodynamics, statics, and mechanics of materials. Eventually my company wanted me to teach their engineers the application of engineering principles to product safety engineering, which I did up to the time I formally retired after 36 years. Subsequently my company asked me to come back as an independent contractor to continue teaching their engineers, which I did for another ten years. So it all came full circle, fulfilling my love of teaching and engineering, the opportunities for which I am eternally grateful.
Now in order to keep my mind active and to continue learning, I am a contributor to this site. In the process of trying to help others in various subjects, I have in turn learned from others and it has expanded my knowledge greatly.