Magellan Sportrak Time error!?

[+skydog5]

Anybody have any info on the clock accuracy of a Magellan Sportrak Pro? I have checked the clock on this thing against WWV and NBS time and it is a whole 2 minutes slow! The navigation is not affected, only the time display. I know the clocks on the satellites are accurate down to the nanosecond. There is one possible error I know of involving leap seconds, and that produces a maximum error of about 12 seconds. I called Tech Support and they just said, "Yeah, they do that. It could be off by as much as 3 Minutes." But how can this be and still navigate?? Anybody else out there with a Magellan product or any other GPS exhibiting this kind of behavior?

[+fizzymagic]

It's going to be exactly two minutes slow. What you're seeing is a "feature" that allows it to deal with time zones that are not exact hours (and yes, there is at least one of those...).

 

It's easy to fix, though. Just go to Setup->Clear Memory->All to basically completely re-set the unit. Then re-initialize it and be sure to enter the proper time (minutes) when you do. From then on, it will be fine.

[Kerry.]

The clock time has no bearing on the capacity to navigate, it simply tells the time and nothing more. Telling one the time isn't a great priority for these type of GPS units as it generally worries more about doing other things.

 

However 2 minutes isn't what one would call normal either and the leap seconds (13 of them) should be a problem either if handled properly.

 

Generally when initializing a rough time is all that's required then the unit will adjust the appropraite/approx time from the navigation message and received data. 2 seconds can be normal but 2 minutes? isn't a system problem either.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+Cornix]

quote:

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Originally posted by fizzymagic:

It's going to be _exactly_ two minutes slow. What you're seeing is a "feature" that allows it to deal with time zones that are not exact hours (and yes, there is at least one of those...).

---

Can't believe this - any proof for your claim?

 

The GPS data contains information that allows a receiver to convert GPS Time into Universal Time (UTC/GMT). To get the time for a specific time zone you only have to add or subtract an offset.

 

Cornix

[+skydog5]

If the satellites have VERY accurate clocks, and the time signal is essential to navigation, and the satellite sets the time on the reciever, them the reciever knows the correct time and is not displaying it correctly.

 

"The clock time has no bearing on the capacity to navigate, it simply tells the time and nothing more. Telling one the time isn't a great priority for these type of GPS units as it generally worries more about doing other things."

[+Prime Suspect]

quote:

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Originally posted by skydog5:

If the satellites have VERY accurate clocks, and the time signal is essential to navigation, and the satellite sets the time on the reciever, them the reciever knows the correct time and is not displaying it correctly.

 

"The clock time has no bearing on the capacity to navigate, it simply tells the time and nothing more. Telling one the time isn't a great priority for these type of GPS units as it generally worries more about doing other things."

---

The point they were making is that updating the clock output has a low CPU priority. But that should only cause the displayed time to be behind a few seconds, not minutes. That was definitely a blow-off answer he gave.

 

"Don't mess with a geocacher. We know all the best places to hide a body."

[+Cornix]

The question is how often the time displayed is synchronized with the GPS time. If this happens only when you turn on your receiver there may be a slight difference after a while, but not 2 minutes.

 

Cornix

[+fizzymagic]

quote:

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Originally posted by Cornix:

Can't believe this - any proof for your claim?

---

Yes.

[+Cornix]

quote:

---

Originally posted by fizzymagic:

It's easy to fix, though. Just go to Setup->Clear Memory->All to basically completely re-set the unit. Then re-initialize it and be sure to enter the proper time (minutes) when you do. From then on, it will be fine.

---

If this is right, it means that GPS time and displayed time NEVER get synchronized.

 

I've always thought the values for time and location that you can enter during initialization are only hints for the receiver and get overwitten with the exact values as soon as the sats are locked.

 

Cornix

[+fizzymagic]

quote:

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Originally posted by Cornix:

If this is right, it means that GPS time and displayed time NEVER get synchronized.

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Sigh.

 

This is not rocket science, folks. It's a minor bug in the Sportrak software.

 

If you display the time on the unit as UTC, it is correct. It only appears off by an integral number of minutes on the local time display.

 

The reason for this is that the local time is affected by the time zone offset. This offset is not always an integral number of hours. So, the software designers apparently chose to synchronize the local time to the nearest minute upon initialization. As I said above, the UTC time in the unit is correct, and the seconds are correct, but the local time is off by an exact number of minutes. This would not normally be a big deal, but the software does not let you re-adjust the minutes without re-initializing the whole thing.

 

So, once again, The clock is not off! Only the local time display is off!

 

The software should probably have synchronized to the nearest 30 minutes instead of minute, and it should allow you to change the minutes offset without a complete reinitialization. But all this discussion about the priority of the time update, etc. is completely irrelevant to the problem at hand.

[+Cornix]

So it's a kind of rounding error, why didn't you say this earlier?

 

Cornix

[Kerry.]

quote:

---

Originally posted by skydog5:

If the satellites have VERY accurate clocks, and the time signal is essential to navigation, and the satellite sets the time on the reciever, them the reciever knows the correct time and is not displaying it correctly.

---

 

As was mentioned time (in this type of unit) is not a priority but also there is a major difference between what could be called "time" and "timing".

 

As it appears it does have something to do with the particular receiver but one would expect straight UTC time to ok.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[Kerry.]

quote:

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Originally posted by Cornix:

So it's a kind of rounding error, why didn't you say this earlier?

---

 

Rounding error some might call it a bug, some might also call it a stuff up as it simply shouldn't do what it's doing.

 

Cheers, Kerry.

 

I never get lost everybody keeps telling me where to go

[+skydog5]

Quote from Fizzymagic:

If you display the time on the unit as UTC, it is correct. It only appears off by an integral number of minutes on the local time display

 

No it's not. I checked. However, your advice about clearing memory worked, as long as I inputted the EXACT time to start with. I think what happens is it only synchronizes seconds, because the clock DOES reset when you re-initialize.

[+Cornix]

quote:

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Originally posted by fizzymagic:

It's going to be exactly two minutes slow.

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quote:

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Originally posted by skydog5:

I think what happens is it only synchronizes seconds, because the clock DOES reset when you re-initialize.

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My receiver was exactly 100 seconds slow (1:40 minutes). So I think we need a new theory.

 

Cornix

[+apersson850]

Seems to be a Magellan thing only. The time indicated on my Garmin Vista isn't off like that, compared to for example my radio controlled clock.

 

Anders

[+bunkerdave]

I know this topic has been dead for a while, but did we ever determine if GPS units actually display the time as transmitted to them and synchronized continuously by the satellites?

 

I have watched this closely since I got my Magellan Map330 some time ago, and have noticed that my cell phone and my GPS are ALWAYS in perfect synchronization. I am not sure if all carriers sync phones this way, I use Verizon, but I do know that when I do take a moment to watch my GPS clock and the clocks on both of my cell phones, they all have precisely the same time - yes, down to the second. I have done this with as many as 6 Verizon cell phones and three GPS units, different makes and models, and noticed the same thing. So...there is clearly a synchronization function at work. I like that. Keeps me out of hot water with the boss.

[+phantom4099]

Two min is kind overkill for being wrong, but I suppose it can happen. And like Kerry said the time the GPS displays is not the highest priority (altough the time used for the location calculation is more accurate). Sometimes clearing the memory does help your problem (but it will probably come back with time).

 

Magellan allows 15 min time (e.g 8:05, 8:20, 8:35, and 8:50) offset to counter act certain time zones (I just saw the other day one country that had this, but for the life of me I can't remember which).

 

Wyatt W.