NAME Time::UTC_SLS - UTC with Smoothed Leap Seconds DESCRIPTION Coordinated Universal Time (UTC) is a time scale with days of unequal lengths, due to leap seconds, in order to keep in step with both Terran rotation (Universal Time, UT) and International Atomic Time (TAI). Some applications that wish to use a time scale that maintains both of these relations can't cope with unequal day lengths, and so cannot use UTC properly. UTC with Smoothed Leap Seconds (UTC-SLS) is another option in such cases. UTC-SLS is a time scale that usually matches UTC exactly but changes rate in the time leading up to a leap second in order to make every day appear to be exactly the same length. On a normal UTC day, of length 86400 UTC seconds, UTC and UTC-SLS behave identically. On a day with a leap second, thus having 86401 or (theoretically) 86399 UTC seconds, UTC and UTC-SLS behave identically for most of the day, but the last 1000 UTC seconds correspond to 999 or (theoretically) 1001 UTC-SLS seconds. Thus every UTC-SLS day has exactly 86400 UTC-SLS seconds. UTC and UTC-SLS are equal on every half hour, and in particular the day boundaries (at midnight) are in the same place on both time scales. See for further explanation. UTC-SLS is defined for the post-1972 form of UTC, using leap seconds. The prior form, from 1961, using `rubber seconds' as well as leaps, could be treated in a similar manner, but the exact algorithm has not been defined. The rubber seconds system was itself trying to achieve part of what UTC-SLS does. This module represents instants on the UTC scale by the combination of a day number and a number of seconds since midnight within the day. In this module the day number is the integral number of days since 1958-01-01, which is the epoch of TAI. This is the convention used by the "Time::UTC" module. Instants on the UTC-SLS scale are represented by a Modified Julian Date, which is a fractional count of days since 1858-11-17T00Z. The MJD is a suitable interchange format between date-manipulation modules. All numbers in this API are "Math::BigRat" objects. All numeric function arguments must be "Math::BigRat"s, and all numeric values returned are likewise "Math::BigRat"s. INSTALLATION perl Build.PL ./Build ./Build test ./Build install AUTHOR Andrew Main (Zefram) COPYRIGHT Copyright (C) 2006, 2007, 2009 Andrew Main (Zefram) LICENSE This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.