"The Resource Unit Leader or RESL is responsible for maintaining the status of all assigned resources (primary and support) at an incident. This is achieved by overseeing the check-in of all resources, maintaining a status-keeping system indicating current location and status of all resources, and maintaining a master list of all resources (key supervisory personnel, primary and support resources, etc.)."
Coffee Break Training - Command and Control Series No. CC-2014-1
United States Fire Administration: http://www.usfa.fema.gov/