:(1) In "The Physical Basis of the Leap Second", by D D McCarthy, C Hackman dan R A Nelson, in Astronomical Journal, vol.136 (2008), pages 1906–1908, it is stated (page 1908), that "the SI second is equivalent to an older measure of the second of UT1, which was too small to start with dan further, as the duration of the UT1 second increases, the discrepancy widens."
(2) Pada akhir 1950-an, piawaian caesium digunakan untuk mengukur both the current mean length of the second of mean waktu suria (UT2) (measured over a period of about a year) (hasil: 9192631830 kitaran, probable error not stated), dan juga saat waktu efimeris (ET) (measured over a period of about 3 years) (hasil:9192631770 ± 20 kitaran): lihat "Time Scales", by L. Essen, in Metrologia, vol.4 (1968), pp.161–165, on p.162. As is well known, the 9192631770 figure was chosen for the SI second. L Essen in the same 1968 article (p.162) stated that this "seemed reasonable in view of the variations in UT2".
L Essen, "Time Scales", Metrologia, vol.4 (1968), pp.161–165, at p.162.
livescience.com
"Extra Second Will be Added to 2005". LiveScience. Dicapai pada November 26, 2009. "dan then, in 1999 for reasons still unknown, the rotation of the Earth speeded up a bit, so we haven't had to add a second since then," O'Brian told LiveScience in a telephone interview.
