UTC, Universal Coordinated Time, is not the the fundamental quantity. It is obtained from TAI, International Atomic Time, by [sometimes] adding|subtracting leap seconds immediately before midnight on June 30 and/or December 31, as specified by the IERS, International Earth Rotation and Reference System Service.
This adjustment is conceptually trivial, but it is sometimes botched; even more curiously, a misbegotten conscious decision to omit it is sometimes taken. However these things may be, UTC is always a derived quantity. TAI is the measured one. Moreover, a surrogate for TAI is what the z/Architecture STCKE and STCK machine instructions make available. Assorted system services may make UTC or UTC ± <local-time offset> available, but they do so only after non-trivial further processing. John Gilmore, Ashland, MA 01721 - USA ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
