On June 30, 1981, the "minute" extending from 10:59 to 11:00 a.m. was extended to include 61 seconds. This leap second was introduced to compensate for the fact that the earth's rotation rate is slowly decreasing. my note: learn more at http://tycho.usno.navy.mil/leapsec.html "Since the first leap second in 1972, all leap seconds have been positive and there were 22 leap seconds in the 27 years to January, 1999. "