The city commission shall appoint an officer of the city who shall have the title of city manager and shall have the powers and perform the duties in this Charter provided. He shall be chosen solely on the basis of his executive and administrative qualifications with special reference to his actual experience in, or his knowledge of, accepted practice in respect to the duties of his office as herein set forth. At the time of his appointment, he need not be a resident of the city or state, but during his tenure of office he shall reside within the city.