[1] Terrestrial Time - Wikipedia, the free encyclopedia (2016-09-07 02:21:55 +09:00) https://en.wikipedia.org/wiki/Terrestrial_Time

[2] 国際原子時 - Wikipedia (2017-01-14 21:10:59 +09:00) https://ja.wikipedia.org/wiki/%E5%9B%BD%E9%9A%9B%E5%8E%9F%E5%AD%90%E6%99%82