Leap Seconds

Leap Seconds


Periodically a "Leap Second" is inserted into or removed from the UTC timescale to keep it in alignment with the rotation of the earth. This may be done on June 30 or December 31 at the last second of the day. The practice thus far has been to add seconds; a subtraction has never been needed. The behavior of various GPS Clock products during Leap Seconds (for current firmware versions) is described below. The sequence output by the clock does not follow the NIST defined sequence for reasons which include pipeline delays to facilitate certain time offset features (which may differ by product), plus the fact that the unit does not receive advance information on upcoming Leap Seconds. In addition, the "60" which is transmitted by GPS is considered an illegal value for purposes of our Time Code outputs and for the input requirements of various types of customer equipment. The typical GPS and Master Clock sequences for the usual Positive Leap Second are as follows: