A Meridian GPS puzzle

[+blindleader]

Does your Meridian GPS display the correct time?

 

If not, how fast or slow is it?

 

What software version is it running?

[Kerry.]

How fast or slow do you need it to be

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Stunod]

Your GPS, once it has locked onto the sats, is probably the most accurate clock you'll ever see. It is constantly corrected by atomic clocks on the sats.

 

"Just because I don't care doesn't mean I don't understand."

[Kerry.]

quote:

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Originally posted by Stunod:

Your GPS, once it has locked onto the sats, is probably the most accurate clock you'll ever see. It is constantly corrected by atomic clocks on the sats.

---

 

It certainly has that possibility but generally since the time of day function has nothing to do with other more critical functions of the receiever, the CPU doesn't pay to much attention to constantly monitoring parts of the Nav message. The time display "in general" can be around 0.5 seconds (sometimes up to 2 seconds) behind (generally always behind in recreational type receivers). It's close enough but not perfect.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+phantom4099]

Well you can manually set the hour, and 15 min offsets. However, I noticed a 2 second delay compared to most other receivers. It is just the displayed time (low priority), and internally it should be set right.

 

Wyatt W.

 

The probability of someone watching you is directly proportional to the stupidity of your actions.

[+phantom4099]

Well I see Kerry beat me to the punch by a couple of min.

 

Wyatt W.

 

The probability of someone watching you is directly proportional to the stupidity of your actions.

[dave and jaime]

being in a non-stabdard time zone i have to adjust my time by 30mins to compensate for newfoundland time.

 

'Get to the point---speak English!!!!'

[John E Cache]

GPS's are on a free running atomic clock that isn't adjusted for leap seconds. The GPS time is 13 seconds off. I don't know if the GPS units adjust the time accordingly.

 

Clocks

 

Charts

[Kerry.]

quote:

---

Originally posted by John E Cache:

GPS's are on a free running atomic clock that isn't adjusted for leap seconds. The GPS time is 13 seconds off. I don't know if the GPS units adjust the time accordingly.

---

 

The leap second difference is also part of the Nav message and GPS receivers do take that into account when determining "current" UTC time.

 

GPS time = UTC time @ Jan 5/6, 1980.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[John E Cache]

quote:

---

Originally posted by Kerry:

 

The leap second difference is also part of the Nav message and GPS receivers do take that into account when determining "current" UTC time.

 

GPS time = UTC time @ Jan 5/6, 1980.

---

 

I assume you talking about the digital message from the Naval Observatory. Are you saying that the GPS units receive leap second information from the satellites too? Or do the GPS manufacturers program the GPSs with the current count since 1980?

[Kerry.]

quote:

---

Originally posted by John E Cache:

I assume you talking about the digital message from the Naval Observatory. Are you saying that the GPS units receive leap second information from the satellites too? Or do the GPS manufacturers program the GPSs with the current count since 1980?

---

 

No not directly from the Naval Observatory but from the actual Navigation message transmitted from the Sats. This information is uploaded from the GPS control centre.

 

"GPS Time" hasn't changed since 1980 but UTC effectively has since the earth has been slowing down so leap seconds are irregularily required to keep time ("earth time"). It just so happens that all leap second adjustments since 1980 have been positive but they could have been negative (if the earth started revolving faster).

 

GPS receivers are programed to read the leap second adjustment from the Nav message and make the appropriate adjustment to GPS time to current UTC time then the user sets their time zone to display local time.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go