TUTORIAL: Time Standard



General Time and Frequency Questions     

The Indonesian Time is realized based on UTC(KIM). 
That are,
Waktu Indonesia Barat:    WIB  =  UTC(KIM) + 7 h
Waktu Indonesia Tengah: WITA = UTC(KIM) + 8 h, and
Waktu Indonesia Timur:    WIT   = UTC(KIM) + 9 h

UTC(KIM) is physical UTC realized at National Standard Time & Frequency Laboratory of Puslit KIM - LIPI. The time keeping system is supported by an ensemble of Cesium Clocks and GPS Time Transfer system that implements BIPM Common View Schedule to keep the UTC(KIM) close to the UTC in microsecond order

Coordinated Universal Time (UTC) is the basis for legal time worldwide and follows TAI (see below) exactly except for an integral number of seconds, presently 33 (since 2006-01-01). These leap seconds are inserted on the advice of the International Earth Rotation Service (IERS) (http://hpiers.obspm.fr/) to ensure that, on average over the years, the Sun is overhead within 0.9 seconds of 12:00:00 UTC on the meridian of Greenwich. UTC is thus the modern successor of Greenwich Mean Time, GMT (see below), which was used when the unit of time was the mean solar day.

International Atomic Time (TAI) is calculated by the BIPM from the readings of more than 200 atomic clocks located in metrology institutes and observatories in more than 30 countries around the world. TAI is made available every month in the BIPM Circular T ( BIPM estimates that TAI does not lose or gain with respect to an imaginary perfect clock by more than about one tenth of a microsecond (0.0000001 second) per year.

Greenwich Mean Time (GMT) is equivalent to universal time (UT). GMT is the "civil" name for the standard; UT is the "scientific" name for the same standard. The distinction between UTC and UT is that UTC is based on an atomic clock (i.e TAI) and UT is based on astronomical observations, which for all practical purposes is an invisibly fine hair to split. Because the earth's rotation is not uniform (it slows down and speeds up in complicated ways), UT does not always flow uniformly. Leap seconds are introduced as needed into UTC so as to keep UTC within 0.9 seconds of UT1, which is a version of UT with certain corrections applied.

Please note that the time displayed in this page may be affected by transmission delay, and by any workload of your computer. It is also possible that the time displayed can be affected by your own Java Virtual Machine.

Note: Java Virtual Machine (VM) is excluded in Internet Explorer 6 (bundled in Window XP). If your system is unable to start the Applet, you have to download & install the Microsoft JavaVM.




Laboratory Profile

General Time and Frequency Questions    

created by cak Anang Chusno Trijanto
last edited:  2006-02-07