[1] 時刻系 - Wikipedia (2017-01-14 21:52:01 +09:00) <https://ja.wikipedia.org/wiki/%E6%99%82%E5%88%BB%E7%B3%BB#.E5.9C.B0.E5.BF.83.E5.BA.A7.E6.A8.99.E6.99.82.EF.BC.88TCG.EF.BC.89>

[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>