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Re: How to set that *(% clock

Posted: Fri Nov 08, 2013 2:23 am
by cwerdna
planet4ever wrote:I have been mildly curious as to what the external standard is. If it really is GPS, they should be good indefinitely, right?...

If it is GPS, I suppose it could be off if the US military screws it up (more info at http://tycho.usno.navy.mil/gps.html, haven't had time to read it). But, then I'd imagine if it were really screwed up, much of or the entire GPS system might not work properly.

Re: How to set that *(% clock

Posted: Fri Nov 08, 2013 2:48 am
by gbarry42
If you are referring to "selective availability", that was turned off in May of 2000. I suppose they could do something unusual for national security purposes, but that would be pretty extraordinary. Given the usefulness of the system and widespread adoption, they can't really mess with it anymore. I don't even hear aircraft pilots saying never to rely on the thing, something they used to do in the past.

In May 2000, at the direction of President Bill Clinton, the U.S government discontinued its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide.

The United States has no intent to ever use Selective Availability again.

In September 2007, the U.S. government announced its decision to procure the future generation of GPS satellites, known as GPS III, without the SA feature. Doing this will make the policy decision of 2000 permanent and eliminate a source of uncertainty in GPS performance that had been of concern to civil GPS users worldwide.

Re: How to set that *(% clock

Posted: Fri Nov 08, 2013 2:53 am
by cwerdna
^^^
No, I'm not talking about selective availability, which I am familiar with as I got my 1st GPS unit (http://gpsinformation.net/main/mag-330.htm) probably not long after SA was turned off. I knew about the civilian vs. military frequencies and the accuracy differences between each, when SA was on.

I'm talking about them messing up the clocks on the satellites themselves, which would render the constellation overhead useless.

Re: How to set that *(% clock

Posted: Fri Nov 08, 2013 6:15 am
by johnrhansen
Radio waves travel awful fast. Gps uses the speed of light to calculate the receiver's position. The time the signal is sent must be accurate beyond belief for the system to even determine what continent you are on. Even if they put the dither back in, the time accuracy will be plenty good for our dashboard clocks.

Re: How to set that *(% clock

Posted: Fri Nov 08, 2013 8:04 am
by TimLee
johnrhansen wrote:Radio waves travel awful fast. Gps uses the speed of light to calculate the receiver's position. The time the signal is sent must be accurate beyond belief for the system to even determine what continent you are on. Even if they put the dither back in, the time accuracy will be plenty good for our dashboard clocks.

I'm certain the navigation time is based on GPS.
And GPS time is the most accurate time source readily available.
To make GPS work right to start with, it has to adjust for the fact that time progresses slower at the GPS satellite which is moving faster than the surface of the earth. Implementation of GPS was a real world proof of Einstein's theory of relativity.

Re: How to set that *(% clock

Posted: Tue Mar 11, 2014 6:16 am
by KJD
How many people curse this clock setting every spring and every fall ?

Re: How to set that *(% clock

Posted: Tue Mar 11, 2014 8:44 am
by johnrhansen
or just not set it. Since daylight savings time is now most of the year anyway, just put a sticky note next it it in the winter saying it is off an hour.... or move to Arizona.

As for the GPS.. on a recent trip to China, I noticed the GPS on my tablet did not work. It was always off by hundreds of feet. Isn't that selective availability?

Re: How to set that *(% clock

Posted: Tue Mar 11, 2014 9:18 am
by dgpcolorado
KJD wrote:How many people curse this clock setting every spring and every fall ?
Yes, I am plenty tired of the daylight savings time switch. Just pick one or the other and stick with it. If you don't want children going to school in the dark adjust school start times. And the same could be done with work hours if it is a concern. Daylight savings time was kind of fun when I was a kid, after moving from a state where it isn't used (Hawai'i, no surprise). But I got tired of it decades ago.

As for the LEAF clocks. It is simple to make the change once one knows how to do it. So I don't get all the fuss. Figure it out once, or read the detailed explanations here at MNL, and then it is no big deal ever after.

-Curmudgeon

Re: How to set that *(% clock

Posted: Tue Mar 11, 2014 9:57 am
by hill
dgpcolorado wrote:Yes, I am plenty tired of the daylight savings time switch. Just pick one or the other and stick with it.
We could all live in Arizona to avoid DST ... only our way too quickly diminishing battery capacity would degrade even quicker. :?
.

Re: How to set that *(% clock

Posted: Tue Mar 11, 2014 10:08 am
by johnrhansen
DST is kind of annoying, kind of like people who set their clocks 5 minutes fast to avoid being late and then tell you the clock is 10 minutes fast so they don't need to hurry