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International standard date and time notation (0 words) |
 | In this case, the Sunday of W52 of the worst case year is day number 4+51*7=361 and 361-366=5 days of W53 belong still to this year, which guarantees that in the worst case year day 4 (Thursday) of W53 is not yet in the next year, so a week number 53 is possible. |
 | Leap years are years with an additional day YYYY-02-29, where the year number is a multiple of four with the following exception: If a year is a multiple of 100, then it is only a leap year if it is also a multiple of 400. |
 | A single leap second 23:59:60 is inserted into the UTC time scale every few years as announced by the International Earth Rotation Service in Paris, to keep UTC from wandering away more than 0.9 s from the less constant astronomical time scale UT1, which is defined by the actual rotation of the earth. |