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Published online by Cambridge University Press: 03 August 2017
A fundamental dynamical scale, ET(solar), was formed from absolute, meridian circle observations, from 1835 to 1982. At 1967.0 the ET(solar) and SI seconds were equal to 1 part in 109 and, from Morrison's (1979 a) ET(lunar) scale, the ET(ILE) and SI seconds were equal to 1 part in 1010. The long term fluctuation in the Earth's rotation has been parabolic, instead of sinusoidal, for at least 350 y.