Cal. Bus. & Prof. Code § 6731.6

Mechanical engineering is that branch of professional engineering described in Section 6734.2 that deals with engineering problems relating to generation, transmission, and utilization of energy in the thermal or mechanical form and also with engineering problems relating to the production of tools, machinery, and their products, and to heating, ventilation, refrigeration, and plumbing. It is concerned with the research, design, production, operational, organizational, and economic aspects of the above.