# Coordinated Universal Time

Coordinated Universal Time (UTC) is a time scale that is kept by time laboratories around the world and is determined by highly precise atomic clocks. The UTC time is accurate to approximately a nanosecond (billionth of a second) per day. UTC is based on the current Gregorian year and is located at 0 degree latitude, the Prime Meridian.

Gregorian UTC is used as the starting point to calculate the system time. To calculate the system time from UTC, the system's offset from UTC is added to UTC. The offset specifies the number of hours and minutes that the system is either west or east of UTC. Everything west of the Prime Meridian has a negative offset and everything east has a positive offset. Then, the offset is applied to UTC to calculate the system time. The system time is displayed in the Time of day system value.

For systems observing a non-Gregorian calendar, the Year offset value is applied to the UTC year to calculate the local system year. For example, if the time zone description specifies a Year offset value of -57, then the local system year is the current Gregorian year minus 57.

The following figure shows where UTC is located relative to System A. UTC has a time value of 4:00 p.m. System A is located in the United States of America in the Central Standard Time zone. System A is located west of UTC 6 hours. Therefore, System A is offset from UTC by -06:00 hours. To calculate System A's system time, add a negative 6 hours (-06:00) to 4:00 p.m., which is the current time value for UTC. With this calculation, System A's local system time is 10:00 a.m.