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1971 Nature 11 June 345/1 An adjustment will be made to all GMT time signal emissions on January 1, 1972, so that a GMT time of 0 h 0 m 0 s will correspond exactly to an IAT time of 0 h 0 m 10 s; thereafter ‘leap seconds’ will be inserted or omitted as necessary at the end of a particular GMT month... From then on, GMT will always be exactly 10 s slow compared with IAT. A so-called positive leap second will begin at 23 h 59 m 60 s on the last day of the month selected and end at 0 h 0 m 0 s on the first day of the next month; by contrast, if the leap second is negative, 23 h 59 m 58 s will be followed one second later by 0 h 0 m 0 s.

1972 Daily Tel. 28 Dec. 10/2 Shortly before 11 p.m. on Sunday (4 a.m. New Year's Day in Britain) technicians at the United States National Bureau of Standards in Boulder, Colorado, will add one leap second to America's atomic clock to correct it to match the Earth's rotation.

1973 Nature 21 Dec. 444/1 Currently, the Earth loses about 3 ms a day on Atomic Time, and the leap seconds are added where necessary..to keep ut and Atomic Time in close correspondence.