37 Repair and maintenance of power plants, steelworks, chemical plants, petroleum plants, telecommunication installations, and traffic control centers and towers; repair and maintenance of computers, computer peripherals, electricity distribution and control machines and instruments, generators, motors, elevators, air-conditioners, telecommunication machines, other than telephone sets, radio receivers and television receivers, metal working machines, and water purifying machines; providing repair and maintenance information in the fields of power plants, steelworks, chemical plants, petroleum plants, telecommunication installations, traffic control centers and towers