 Skyscrapers provided a wide range of in-house services for their tenants, including shops, restaurants, barbers, tobacconists, newsagents, tailors, professional specialists and libraries.Skyscrapers also employed a substantial number of service staff to maintain and support them; a building such as the Chicago Board of Trade spent 20 percent of its rental revenue on service staff, employing 41 people, including janitors, elevator operators, engineers, and an electrician.With this collection of services and facilities, skyscrapers of the period were often referred to as small cities in their own right.