List of UTC timing centers is a list of over 70 recognized maintainers of atomic clocks around the world from which UTC is calculated. Below are links to some of the more notable time centers which contribute to the calculation of UTC. UTC is calculated by the International Bureau of Weights and Measures (BIPM) using weighted averages of the various times as reported by these 70+ listed timing centers. BIPM lists the time differences between the UTC timing centers in a monthly publication called Circular T, which contains the most up to date list of contributors to UTC.