I am in EST zone which is 5.0 hours from GMT/UTC. GPS time is 18 seconds ahead of UTC due to “leap seconds”. So if the nav was not making the time zone correction the time synced to GPS should be 5 hours and 28 seconds ahead. I’ll go check and see what it is. If anyone knows where a menu option is to set the time zone, please tell me where it is. I couldn’t find it.
If it is still wrong, I’ll tty the reset.
I reviewed the 8.4 manual and notice the software program is supposed to update the time for your time zone so you won't find the setting; just the manual set and GPS link set. So this points strongly to update error or incomplete processing.
As far as leap seconds, they are already accounted for in the broadcast time signal - or receiver software:
Atomic Time vs. Universal Time
2 components are used to determine
UTC (Coordinated Universal Time):
- International Atomic Time (TAI): A time scale that combines the output of some 200 highly precise atomic clocks worldwide, and provides the exact speed for our clocks to tick.
- Universal Time (UT1), also known as Astronomical Time, refers to the Earth's rotation around its own axis, which determines the length of a day.
Before the difference between UTC and UT1 reaches 0.9 seconds, a leap second is added to UTC and to clocks worldwide. By adding an additional second to the time count, our clocks are effectively stopped for that second to give Earth the opportunity to catch up.
Upcoming leap seconds are announced by the International Earth Rotation and Reference Systems Service (IERS) in
Paris, France.
The Science Behind Leap Seconds
Atomic Time Too Accurate
The reason we have to add a second now and then is that the velocity of Earth's rotation around its own axis does not match the speed of atomic time. On average, it is a tiny bit too slow—and it is gradually slowing down, although very slightly.
Atomic clocks, however,
tick away at pretty much the same speed over millions of years. Compared to the Earth's rotation, atomic clocks are simply too consistent.
How Often Are Leap Seconds Added?
Before the first leap second was added in 1972, UTC was 10 seconds behind Atomic Time. So far, a total of
27 leap seconds have been added. This means that the Earth has slowed down an additional 27 seconds compared to atomic time since then.
However, this does
NOT mean that the days are 27 seconds longer nowadays. The only difference is that the days a leap second was added had 86,401 seconds instead of the usual 86,400 seconds.
Last Leap Second in December 2016
The last leap second was added on December 31, 2016, at 23:59:60 UTC. The difference between
UTC and
International Atomic Time (TAI) increased from the 36 seconds to the current 37 seconds.
Next Leap Second
Based on current predictions, the next leap second should be added on June 30, 2020. However, since the speed of the Earth's rotation is subject to unpredictable short-term variations, the date may still change. Once it is officially announced, we will publish it in our
Time Zone News.
And, to overload to the
"Way" TMI (too much information) factor:
Timekeeping [edit]
Leap seconds[edit]
While most clocks derive their time from
Coordinated Universal Time (UTC), the atomic clocks on the satellites are set to GPS time (GPST; see the page of
United States Naval Observatory). The difference is that GPS time is not corrected to match the rotation of the Earth, so it does not contain
leap seconds or other corrections that are periodically added to UTC. GPS time was set to match UTC in 1980, but has since diverged. The lack of corrections means that GPS time remains at a constant offset with
International Atomic Time (TAI) (TAI − GPS = 19 seconds). Periodic corrections are performed to the on-board clocks to keep them synchronized with ground clocks.
[148]
The GPS navigation message includes the difference between GPS time and UTC. As of January 2017,
[update] GPS time is 18 seconds ahead of UTC because of the leap second added to UTC on December 31, 2016.
[149] Receivers subtract this offset from GPS time to calculate UTC and specific timezone values. New GPS units may not show the correct UTC time until after receiving the UTC offset message. The GPS-UTC offset field can accommodate 255 leap seconds (eight bits).
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