# Accurate watches



## **DONOTDELETE** (Nov 20, 2001)

I'm always interested in very accurate watches. I got one of those radio ones once, but it rarely picked up the signal so I returned it. Since I will soon move to Hawaii, I don't think even the radio clocks work out there.

My present watch is a Timex Expedition. I've had it for years and it started out keeping extraordinary time - the first 50 day it lost less than a quarter second! Then it started to run gradually faster and now it gains a second every 3 to 3.5 days. Very good, but I'd be happy to find something better at a decent price.

I'm not into the big watches that are supposed to be extra tough (not that I want something easiy broken). This one is about as large as i would want.

Aside from accurate time, I only seriously need the following:

Stop watch - pretty standard.

Alarms - LOTS of them. I once had one with 60, which is more than I need, but I can easily use 6-10.

Ability to easily read the dial - Indiglo is acceptable. Some watches that used a different light were too hard to read and it seem that their light killed battery power faster.

Any recommendation?

One other thing, about the alarms. The 60 alarm watch was nice, but not consumer friendly.

I'd like to see a watch that let you specify when it would go off (once a week, every day, every week day, etc). I can imagine the interface - just have 7 positions you can mark or unmark, representing what days you want it to work.

Also, there should be some kind of easier temporary deactivation, either by turning them all off at once or perhaps having "banks" of alarms (perhaps 10 in each if you have 60 alarms) which allows you turn turn off or on a bank at a time.

Anyway, those are my ideas. Does anything come close?

Bob


----------



## busbar (Nov 21, 2001)

Have you considered 100ns accuracy? http://www.arbiter.com/pdf/ds_1088b.pdf will run on 12 volts with the appropriate power supply.


----------



## **DONOTDELETE** (Nov 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by busbar:
*Have you considered 100ns accuracy? http://www.arbiter.com/pdf/ds_1088b.pdf will run on 12 volts with the appropriate power supply.*<HR></BLOCKQUOTE>

Interesting. But I did a quick scan and couldn't find anything about prices.

Bob


----------



## Spidey82 (Nov 21, 2001)

Swatch watch seems quite accurated,
my nokia phone is still on the dot after months(nearly a year).
Linfeng


----------



## **DONOTDELETE** (Nov 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Spidey82:
*Swatch watch seems quite accurated,
my nokia phone is still on the dot after months(nearly a year).
Linfeng*<HR></BLOCKQUOTE>

What are swatches guaranteed at? I checked with Timex not long ago and was surprised that they were guaranteed to be within 15 seconds a month. My watch right now would take at least 45 days get off that much, but still, that isn't bad.

On the phone, are you sure it doesn't get its time over the phone connection and thus it isn't like a regular time piece?

Bob


----------



## busbar (Nov 21, 2001)

Trebor--

An Arbiter 1088B is ~$3500. Their low-end version is ~$900.


----------



## **DONOTDELETE** (Nov 21, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by busbar:
*Trebor--

An Arbiter 1088B is ~$3500. Their low-end version is ~$900.*<HR></BLOCKQUOTE>

Ouch! Well, cross that off the list!

Bob


----------



## John N (Nov 22, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Trebor:
*On the phone, are you sure it doesn't get its time over the phone connection and thus it isn't like a regular time piece?
*<HR></BLOCKQUOTE>

This appears to be the case with my StarTAC. Normally dead on, when roaming in analong mode it starts to keep very poor time. Much worse than your most inexpensive watch. 

-john


----------



## Spidey82 (Nov 22, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Trebor:
*What are swatches guaranteed at*<HR></BLOCKQUOTE>
The accuracy is not stated, but there is a line which says "Imcomparable precision of quarz for an exceptional degree of autonomy"
my watch is auto quarz. can run for 100 days when fully charge. Charge with body movement.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Trebor:
*On the phone, are you sure it doesn't get its time over the phone connection and thus it isn't like a regular time piece?*<HR></BLOCKQUOTE>
I don't have my auto update on.


----------



## Mike (Dec 7, 2001)

I have a simple Helbros watch that I got for $5 or $10 at a flea market type thing. It is so accurate that I only need to adjust it maybe every 2 years. I runs 4-5 years on a standard alkaline battery.


----------



## **DONOTDELETE** (Dec 15, 2001)

If you are moving to Hawaii, you may want to go back and purchase that radio clock again. WWVH broadcasts from Hawaii so that clock should be plenty accurate since you'll have very little propagation delay.


----------



## **DONOTDELETE** (Dec 17, 2001)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Lurch556:
*If you are moving to Hawaii, you may want to go back and purchase that radio clock again. WWVH broadcasts from Hawaii so that clock should be plenty accurate since you'll have very little propagation delay.*<HR></BLOCKQUOTE>

Unfortunately, that isn't how it works. The broadcast out of Kauai (you can tell which is Kauai and which is Colorado because the Kauai station used a woman's voice) does not include the signal to watches and clocks. Only Colorado has it. I emailed them about it once and they said there would be a problem with the two signals interfering with each other. Apparently the clocks and watches are only set up to deal with one frequency. Also, they said it is costly to setup.


----------



## BuddTX (Jan 16, 2002)

Where to get the accurate time:
www.time.gov


----------



## busbar (Jan 16, 2002)

Maybe a little OT, but how accurate are the time displays in handheld GPS receivers?


----------



## MarcV (Jan 16, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by busbar:
*how accurate are the time displays in handheld GPS receivers?*<HR></BLOCKQUOTE>

Incredibly accurate. GPS transmitters *are* clocks and your receiver decides your location by comparing times among the clocks. The concept is simple, really. I wish I had thought of it!


----------



## Brock (Jan 18, 2002)

It's is funny. GPS's receive time from multiple satellites to figure out where they are and do it by calculating the differences in time from each satellite. Anyway it says on them not to use them as a clock because they could be off by as much as .01 seconds.


----------



## vcal (Jan 18, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Brock:
*It's is funny. GPS's receive time from multiple satellites to figure out where they are and do it by calculating the differences in time from each satellite. Anyway it says on them not to use them as a clock because they could be off by as much as .01 seconds.



*<HR></BLOCKQUOTE>

That accuracy is provided by their Rubidium clocks, which aren't quite as accurate as say, the hydrogen maser, or better yet, the Cesium fountain beam that N.I.S.T. (bureau-standards) uses




(which is accurate to +or- 1 -9_billionth_ of a second), so theoretically, it could be off by a little less than a second in 20 million years.

-So says the New York Times in their Circuits magazine on Jan. 17


----------



## **DONOTDELETE** (Jan 26, 2002)

My current watch gains about 2+ seconds per month, (gaining is better than losing with this watch, since I can reset the seconds to 00 easily and don't have to futz with the minutes) it's a Breitling. My best watch in terms of accuracy is a "Micronta" (a.k.a. National Semiconductor) that loses less than 5 seconds per *year*. Just a fluke I think--But it's so good I just don't set it except for battery changes. I've had it running since the late 70's. Neither watch has all the alarms you want


----------



## Wingerr (Apr 18, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Trebor:
*I'm always interested in very accurate watches. 
Aside from accurate time, I only seriously need the following:
Stop watch - pretty standard.
Alarms - LOTS of them. I once had one with 60, which is more than I need, but I can easily use 6-10.
Ability to easily read the dial - Indiglo is acceptable. Some watches that used a different light were too hard to read and it seem that their light killed battery power faster.

Any recommendation?
I'd like to see a watch that let you specify when it would go off (once a week, every day, every week day, etc). I can imagine the interface - just have 7 positions you can mark or unmark, representing what days you want it to work.

Also, there should be some kind of easier temporary deactivation, either by turning them all off at once or perhaps having "banks" of alarms (perhaps 10 in each if you have 60 alarms) which allows you turn turn off or on a bank at a time.

Anyway, those are my ideas. Does anything come close?

Bob*<HR></BLOCKQUOTE>

The Timex Internet Messenger watch seems to meet nearly all the requirements you listed, except that it only has 5 alarms, and the display is rather chock full of information, which makes it harder to read quickly.
Very accurate time since it picks up the time signal from the pager network, and yes, it should work in HI.
Alarms can be set a year in advance to any date, and set to go off daily, weekly, weekends only, weekdays only, or yearly. The alarms can be individually disarmed, but not really in a bank as you wanted.
Stopwatch function can store up to 99 laps and give you the best time (= shortest) out of the bunch-
Timer function will allow for count down from 99 hours, and starts the chronograph at the end of the timer period, so you know how long it's been since the timer ended. (Could be useful to know how many hours your 3 minute egg was actually cooking for).

The time is very precise, and DST is automatically accounted for, as well as your location- if you travel to another city, it will automatically correct your time zone and display the location where you are (could be handy if your friends play a prank on you and drop you off somewhere in another part of the country while you snooze-


----------



## geepondy (Apr 20, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Trebor:
*
On the phone, are you sure it doesn't get its time over the phone connection and thus it isn't like a regular time piece?

Bob*<HR></BLOCKQUOTE>

I can verify this to be so because I recently traveled to a location three time zones away and the phone picked up the local time when I turned it on.


----------



## Darell (Apr 20, 2002)

To answer up a bunch of questions in one:

I can tell you from experience that my atomic clocks, my GPS receiver and my Sprint phone have never been detectably (assuming that is a word) "off" from each other - no matter where I travel. I really do like perfect time, and think this technology should be incorporated in EVERY electronic device we have...


----------



## BuddTX (Apr 20, 2002)

I bought this Elgin watch at Wal-mart for like 45 or 48 dollars, it is one of those watches with both an analog and a digital display.I have tested it twice at two week intervals, and my watch gains only about 4 seconds every two weeks.

I know that this "Elgin" watch is not a real Elgin watch, they stopped making Elgin watches in 1968 or 69. This is just a company that uses their name, but still 4 seconds every 2 weeks. I think that is pretty good!

What do other people get with watch accuracy?


----------



## Wingerr (Apr 20, 2002)

Discounting the self setting watches, my Luminox has gained about 1/2 second since I set it for DST, about two weeks. 

Quartz watches are generally held to different standards than mechanical timepieces-

I've got two atomic clocks, a GPS, and the pager watch to check against- the main problem with using the GPS for time is that the time display has low priority for the processing, so it often doesn't update regularly, and will lag behind the actual time sometimes.


----------



## **DONOTDELETE** (Apr 27, 2002)

> The Timex Internet Messenger watch seems to meet nearly all the requirements you listed, except that it only has 5 alarms <

Well, the many alarms is less critical now since I retired (but still teach part-time). So I have fewer times to keep track of.

> Very accurate time since it picks up the time signal from the pager network, and yes, it should work in HI. <

Do you have to pay for pager access? Since I have no use for a pager, I wouldn't want to pay for accuracy. Also, is the pager time signal very accurate? I know TV time is less dependable than one would think, though it seems to be getting better.

> Alarms can be set a year in advance to any date, and set to go off daily, weekly, weekends only, weekdays only, or yearly. <

Not bad, though just 5 alarms isn't much for all those circumstances. I still wish you could specify particular days of the week since my classes are just MWF. I don't want them going on on tues/thurs.

> The alarms can be individually disarmed, but not really in a bank as you wanted. <

This always amazes me. There are times anyone is in a place where you don't want alarms going off - who wants to turn off even 5 of them one at a time? At the very least, I think there should be a general "OFF" option for all.

> Stopwatch function can store up to 99 laps <

Hey, I could use that - I have taken up bike riding here in Hawaii and time myself riding the 13.5 miles from where I live to Waikiki, but also try to mark certain intermediate points. I don't like to stop to write the times down, but if I can store these as lap times and call up the numbers when the ride is done, that would be great!

> The time is very precise, and DST is automatically accounted for, as well as your location- if you travel to another city, it will automatically correct your time zone and display the location where you are <

Hey, that's neat! I assume it also accounts for places that DON'T have DST (Hawaii doesn't). This may be worth changing watches for, even though it isn't perfect. I've held on to the one I have because it has never done worse than gain 1 second in 3.5 days.

So, how much does this thing cost?


----------



## **DONOTDELETE** (Apr 28, 2002)

Trebor, 

Exactly how much of a "time-aholic" are you?






wingerr has probably found the best overall watch for you. If you want the absolute most accurate watch, other features be damned, get the NEW Casio GPS (PAT-2GP) watch. It sets itself every time it gets a GPS reading to the GPS time signal. Don't get the original one, it couldn't do that. 

In very rough, very general order of accuracy, GPS is more accurate than cellular (GSM, CDMA) which is more accurate than WWVB. 

The GPS system is set every day to the NIST UTC, which is "THE OFFICIAL TIME". A new, good $500 GPS receiver can usually get down to 20 nanoseconds of accuracy with a stationary position and 4 or 5 visible satellites in a good spread-out pattern. One nanosecond of inaccuracy works out to about one foot of error. But, not all receivers will display the actual GPS time signal



which is why you see inaccuracies and lag in the display. For instance, my Garmin GPS has two clocks, a cheap quartz oscillator that drives the displayed time, and the actual GPS-set internal clock, which can only be pulled up through the GPS satellite information display page. Why Garmin did this, I have no idea. 

Of course to get this kind of accuracy, you would probably need to get a GPS that can feed the signal to a PC loaded with the proper software, or just buy one of those $1500 GPS clocks!

Cellular towers broadcast a time signal as part of the telephone transmission, which is usually set at the main office according to a GPS clock. The cell towers use the time signal to "divide" up the time it communicates with each phone in the cell. The cell phone uses that time to know when to communicate with the cell tower. Cell time signals have to be accurate to only within 10 microseconds for the cell phone system ot work. This technology is what made Qualcomm rich. 

WWVB, the atomic time signal, is broadcast at a one microsecond accuracy, per NIST. But, the transmission time to reach your receiver is affected by weather conditions, sun spots, etc. limiting effective accuracy to around one millisecond. Another drawback of WWVB is that it can't tell where in the timezone you are. So it considers the time at the east end of Texas to be the same as the west end of Texas, even though it's about 1000 miles apart. (everybody knows that west Texas is actually 20 years in the past






) 

Bottom line: Most people's most accurate clock is their cell phone. I've got several WWVB clocks and a digital CDMA phone and a digital GSM phone and a good GPS. All show the same time, and all do a good job of telling me when I'm late for work





Of course, YMMV 
Tej, (who is also a time-aholic and gps-aholic)

Check out this list of manufacturers 

Casio GPS watch home page


----------



## Wingerr (Apr 28, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by thetrebor:
*
Do you have to pay for pager access? Since I have no use for a pager, I wouldn't want to pay for accuracy. Also, is the pager time signal very accurate? I know TV time is less dependable than one would think, though it seems to be getting better.*<HR></BLOCKQUOTE>

Well, the promotion currently running from Skytel gives you one year service free with purchase of the watch, but service isn't needed to get the benefits of the automatic time setting-
The time signal has been consistently on the second when compared to my other time references like the atomic clock receivers and GPS-

> Stopwatch function can store up to 99 laps <

> The time is very precise, and DST is automatically accounted for, as well as your location- if you travel to another city, it will automatically correct your time zone and display the location where you are <
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*
Hey, that's neat! I assume it also accounts for places that DON'T have DST (Hawaii doesn't). This may be worth changing watches for, even though it isn't perfect. I've held on to the one I have because it has never done worse than gain 1 second in 3.5 days.
*<HR></BLOCKQUOTE>
Yes, you can set it to ignore DST, so that's no problem.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*
So, how much does this thing cost?*<HR></BLOCKQUOTE>
It's $89.83 from Walmart- (don't get it directly from skytel), or $85 from Timex.com with a 15% discount code for Mother's Day.
One thing to keep in mind though, it uses type 675 hearing aid batteries, and they each last 1 to 2 months according to the specs, when the pager function is enabled (it can be turned on or off without affecting the watch functions). They'll last longer if the pager function is disabled, but then you won't get the time set function either. I'm not sure how much difference in battery life there is when the pager is turned off, but it's probably significant. You could possibly just leave it off most of the time, and just turn it on briefly every now and then to set the time, but that'd be less hands off than you probably want.

Prior post on Timex watch-

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>*
Bottom line: Most people's most accurate clock is their cell phone. 
--
All show the same time, and all do a good job of telling me when I'm late for work *<HR></BLOCKQUOTE>

LOL, same here- it's good to know precisely how late I am for work!
I'm not sure if my TDMA Ericsson cell phone gets the time from the network or not; I usually don't bother using it for a time reference, but I just noticed it's 4 seconds fast from all the other references I have. Whether it's coincidence that it just happens to be that close or if it DOES autoset, but is inaccurate, I don't know-


----------



## **DONOTDELETE** (Apr 30, 2002)

> Exactly how much of a "time-aholic" are you? <

Pretty big! But I am unfortunately grounded by money so its nice to find something cheap ($100 or less ideally). I used to have several atomic clocks on the mainland, but in Hawaii, we don't get the signal. Working with kids who were supposed to be on time to activities, I got tired of the "but my watch says", or "the TV says", etc stuff. So I set my watch regularly by the shortwave time signal and just told them my watch was set by the official time, end of discussion! Solved a lot of problems.

So, I don't need nano-second accuracy because I'm not measuring my geographical position - I just want the right time for time sake and, ideally, not to have to ever reset my watch or clocks! If it is one second off, fine. Two seconds, not fine.

> wingerr has probably found the best overall watch for you. <

I looked it up, but paying for the paging stuff is going to add to the expense so that killed that idea.

> If you want the absolute most accurate watch, other features be damned, get the NEW Casio GPS (PAT-2GP) watch. <

Checked that one too - $500 is way too much!

> Bottom line: Most people's most accurate clock is their cell phone. <

That's good to know. It would be accurate to within a second? I have Sprint.

Thanks.


----------



## **DONOTDELETE** (Apr 30, 2002)

> Well, the promotion currently running from Skytel gives you one year service free with purchase of the watch, but service isn't needed to get the benefits of the automatic time setting <

I noticed the promotion, but don't want to ever deal with pager fees. But I didn't see that it would automatically set the time without that. I guess I better look again to be sure because if I can avoid that expense, I may well get the watch for the time setting and other benefits.

> Yes, you can set it to ignore DST, so that's no problem. <

That's a nice plus.

> It's $99 from skytel or $89.83 from Walmart <

Good price. And I think Walmart has a guarantee that you can return watches after a reasonable time so I could make sure things work the way I want.

> They'll last longer if the pager function is disabled, but then you won't get the time set function either. <

I guess that is an important issue. If the battery lasted a long time without the pager turn on, I could just activate it once every week or so (depending on how well it held its time). But I wouldn't want to hassle with batteries (besides the expense) more than once a year if I could avoid it. I would think the pager takes up a lot of power.

I could have sworn it sounded like you had to have the pager service to set the time though.


----------



## Wingerr (Apr 30, 2002)

It's been confirmed that active pager service isn't needed to set the time- 


After getting the watch and putting the battery in, the time is set within 4 minutes, day, date, year, time, and location to boot. This is all before calling up to activate the service-
I don't think I'll be able to verify too easily how long a battery will last with the pager function off, not until my year is up, anyway...
I forgot to mention, there's an auto mode where you can automatically set the pager function to turn off for a specified period every day; that could actually be well suited for you, since you can just have it turn on for 5 minutes a day, and turn off the rest of the time, automatically. Then you don't have to diddle with the watch at all, and it'll be autosetting on its own! That's what I'll do if I decide not to renew after the year is up- 
If you can find the watch at Walmart, you might just try it out to see if you do in fact receive the time signal where you are, and not activate the service, so that you can return it easily. Once you activate the watch, that particular watch is logged into skytel's system, and the next person won't be able to do it, if you do return it. Each watch has an individual capcode.


----------



## **DONOTDELETE** (May 1, 2002)

> After getting the watch and putting the battery in, the time is set within 4 minutes, day, date, year, time, and location to boot. This is all before calling up to activate the service <

Ah, sounds logical!

> I don't think I'll be able to verify too easily how long a battery will last with the pager function off, not until my year is up, anyway... <

I emailed the Timex folks and asked about that. We'll see if I get an answer - I did get a confirmatio that the post was displayed.

> I forgot to mention, there's an auto mode where you can automatically set the pager function to turn off for a specified period every day <

Oh, that is neat!

> Once you activate the watch, that particular watch is logged into skytel's system, and the next person won't be able to do it, if you do return it. Each watch has an individual capcode. <

Interesting.

I tried checking the Skytel coverage area, but it wasn't very clear. I live in Aiea HI and when I looked at the map, nothing was highlighted, but what was highlighted didn't match the color code they showed. I've only had a pager once and even years ago, in the country, it seemed to almost always be in a coverage area. I don't see why Skytel wouldn't cover pretty much everything here - as best I could tell, it was very blotchy, almost being limited to a few blocks in some areas.

I've gotta get to the Walmart here - there is only one and since I don't have a car, I have to do it by bus.


----------



## Wingerr (May 5, 2002)

If you don't want to trek to Walmart, you can order online from Timex.com
Free shipping (though I don't know about HI), and there's a 15% discount coupon currently available, making it about $85 total.


----------



## **DONOTDELETE** (May 5, 2002)

> and there's a 15% discount coupon currently available, making it about $85 total. <

Thanks!


----------



## **DONOTDELETE** (May 5, 2002)

Looks like they're clearing out an older model for $49 here.


----------



## **DONOTDELETE** (May 14, 2002)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by wingerr:
*It's been confirmed that active pager service isn't needed to set the time- 


After getting the watch and putting the battery in, the time is set within 4 minutes, day, date, year, time, and location to boot. This is all before calling up to activate the service-
I don't think I'll be able to verify too easily how long a battery will last with the pager function off, not until my year is up, anyway...
*<HR></BLOCKQUOTE>

I finally got a response to my question to customer support. The only bad part is about the battery life:

You don't have to have the pager service on to get the time from the Skytel Towers. But the battery life will stay about about 2 months even if you have the pager turned off. The batteries themselves only cost
about a dollar. But I don't know of any other watches that we make that is as accurate as you might want.

Beepwear Help Desk.tm


----------



## **DONOTDELETE** (May 20, 2002)

I purchased a Citizen Skyhawk about 3 months ago (solar, long battery reserve, 3 alarms, chronograph, time zones, titanium). After checking it every month using this site, it's only lost about 3.5 seconds every month. Much better than my old G-Shock that gained around 15 seconds each month.


----------



## PaulDavid (Feb 7, 2007)

*Re: Accurate watches USNO _NOT_ NIST!*

Hi guys -
I have a PAT-2GP, which turns out to be a pretty poor gps really, I have and professionally use many which are far better. I think Casio pushed minaturization too far this time. The PAT-2GP sensitivity is just rotten. It stays in my closet at home... but on to a more important on a misconception posted long ago, below (the time-aholic post)...

NIST does NOT give you time from GPS, and NIST has nothing to do with GPS. GPS is a completely DoD-run facility. NIST monitors GPS, and NIST builds cool small and topnotch clock designs and standands for the Second... and via NTP you can get NIST time (and since USNO turned over WWV to NIST in the 30's you can get it there too, as noted, less accurately). NIST agrees to remain accurate to within 100 nanoseconds of USNO (www.usno.navy.mil), but USNO provides precise time (to below ten nanoseconds) to the GPS constellation, via a thing called TWSTT to the AMC which feeds the USAF control guys in Colorado Springs.

Technically, while GPS receives UTC (USNO), the cesium clocks on board are guided to a sort of free running standard, which also does not normally inject leapseconds (another issue, but which USNO runs and oversees, again, not NIST). So GPS time is very accurate (not the most accurate but the most for 90% of the users), but in all reality gps time can be many (upt ot a dozen) seconds different to the fundamental, true time, UTC (USNO), for operating effectiveness of the gps constellation. And as said, NIST has to be within 100 ns of USNO... Really, most guys don't need 100 nanoseconds (a nanosecond is the time light travels about 1 foot by the way), so above this, it becomes hard to tell the time source, esp with NTP available... But rest assured it all traces back to USNO for GPS, never NIST. Also to clarify the concept - NIST measures the second, and they are outstanding at that; they turn on a clock, measure, then turn off, not requiring robust timekeeping. USNO is a clock; the national clock (run by DoD). USNO also runs by far the largest bank of statistically linked clocks cesium beam, hydrogen maser, rhubidium fountain (and now light clock designs on the board), normally over 120.... Your tax dollars well spent actually...

As an additional note, all world time labs provide weighted precise time inputes to world time (TAI and UTC) at Paris' IBS, parent to NIST (sort of). Many dozens of countries participate, and the precisions/accuracies are heavily analized, and monthly, IBS puts out what the "time was that month", so worldwide labs can re-steer their atomic clocks. Last I checked, NIST is up there (often #2), at about 3% input to world time. USNO runs 40%; ergo essentially steers world time.

You might find these links interesting:
http://tycho.usno.navy.mil/
http://tycho.usno.navy.mil/gps.html
http://tycho.usno.navy.mil/twoway.html
http://tycho.usno.navy.mil/ntp.html
http://tycho.usno.navy.mil/mc_to.html

Hope that helps - GPS takes time from USNO, never NIST. It gets frustrating because USNO is doing an unsung effort with a tiny staff compared to NIST, who has a giant public relations team ...
Best/PaulDavid


----------



## carbine15 (Feb 7, 2007)

*Re: Accurate watches USNO _NOT_ NIST!*



PaulDavid said:


> Hi guys -
> I have a PAT-2GP, which turns out to be a pretty poor gps really, I have and professionally use many which are far better. I think Casio pushed minaturization too far this time. The PAT-2GP sensitivity is just rotten. It stays in my closet at home... but on to a more important on a misconception posted long ago, below (the time-aholic post)...
> 
> NIST does NOT give you time from GPS, and NIST has nothing to do with GPS. GPS is a completely DoD-run facility. NIST monitors GPS, and NIST builds cool small and topnotch clock designs and standands for the Second... and via NTP you can get NIST time (and since USNO turned over WWV to NIST in the 30's you can get it there too, as noted, less accurately). NIST agrees to remain accurate to within 100 nanoseconds of USNO (www.usno.navy.mil), but USNO provides precise time (to below ten nanoseconds) to the GPS constellation, via a thing called TWSTT to the AMC which feeds the USAF control guys in Colorado Springs.
> ...


YOu resurrected a very old thread to make your first post. I'm impressed. Welcome to CPF.


----------



## Rudi (Feb 7, 2007)

Regarding accuracy, I've had watches that ran the same on and off my wrist, and others that run differently. I've observed this with mechanical wind-up movements as well as with battery-powered quartz. Has anyone done such comparative tests?


----------



## cave dave (Feb 11, 2007)

I'm glad he dug this post up. I enjoyed the info in this post, although I have no idea why anyone would need accuracy to within a second or two. (except for cumulative error over the course of a year)

I recently bought some new watches including my first automatic and also got one of those Atomic Radio weather stations so I've been keeping track of accuracy just for curiosity sake. The automatics keep lousy time but I have to reset them ever time a month has less than 30 days anyway.

My 5yr old timex expedition quartz analog has only gained 1 sec in two months. That is amazing and unusual, I guess there is such a thing as the "watch lottery". My recently acquired Seiko 5 auto lost a couple seconds a day in New Mexico but has been gaining a couple sec/day in Virginia.

My cell phone may be "accurate" to within 10 nanosecs but it doesn't display seconds so its not very "precise" (or is it the other way around?)


----------

