Seiko 2J30, Instructions Manual

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INTERCALARY SECOND
(LEAP SECOND)
Normally there are 86,400 seconds in a day. Due to a slight change in the earth's
rotation, extra second may be added to one day during the year. This is called the
intercalary second. Every year the decision is made whether such an adjustment
is needed. When the adjustment takes place, the standard time should be
corrected by delaying the standard time one second. To keep your SEIKO watch
accurate with the world standard time, adjust your watch to a time signal
whenever such adjustment is made.
According to the information from the observatories all over the world, the
standard time is delayed one second simultaneously throughout the world by the
Greenwich Royal Observatory.
In the Greenwich Mean Time, an extra second will be added to the one minute
between 11:59 P.M. and 12:00 A.M. either on December 31st or on June 30th.
In the Japan Time, due to the time differential an extra second will be added to
the one minute between 8:59 A.M. and 9:00 A.M. on January 1st or July 1st.
However, the adjustment may not be made in some years. Please, check by a
newspaper, etc. whether such an adjustment will be made or not.
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