The decision to add a leap second is made by the International Earth Rotation and Reference Systems Service, an international standards body, to accommodate for variations in the Earth’s rotational speed. The US federal government’s Global Positioning System (GPS) broadcasts leap second correction information in the navigation message. However, it is the responsibility of users to assure that their hardware and software recognizes and manages the leap second correctly; errors and equipment failures can occur when GPS receivers and clocks process the leap second signal incorrectly. It is suggested that readers ensure all software and firmware is up to date.

This document is intended to assist federal, state, local, and private sector organizations with preparations for the Saturday, 31 December 2016 Leap Second event. The document is sponsored by the Department of Homeland Security’s National Cybersecurity and Communications Integration Center in coordination with the United States Naval Observatory, National Institute of Standards and Technology, the USCG Navigation Center, and the National Coordination Office for Space-Based Positioning, Navigation and Timing.