# Why are digital watchs so inaccurate?



## HighLight (Apr 1, 2006)

I was browsing the Casio watch site and I noticed the specs for some watchs were like +/-12 seconds per month. Some of the more expensive watchs were a bit better. I'm wondering what makes digital watchs so inaccurate. One would think that with a digital chip and no moving parts (except for the stepper motors for the ones with actual hands) that they would be more accurate than a mechanical watch hands down. Why can't these digital watchs be more accurate, say to the tune of 5-6 seconds a month?


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## PhotonBoy (Apr 1, 2006)

These watches are self-setting and theoretically are never wrong. They don't work in Atlantic Canada though.:mecry:


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## Christoph (Apr 1, 2006)

I think temprature is the biggest culprit in watches.the little electrons like to run at different speeds under different temps.(sounds good to me :devil: )C


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## TinderBox (UK) (Apr 1, 2006)

electronic watches use a crystal to regulate the time, and it runs slightly faster or slower depending on the temprature.

regards.


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## magic79 (Apr 1, 2006)

I think it has more to do with variation in the 32.768 kHz crystal than temperature. Without individual trimming (which I don't think they do) the crystal frequency can be off a few Hz from crystal-to-crystal.

However, compared to automatics (self-wind) they are significantly more accurate. Automatics are +/- 5-10 MINUTES per month.

http://www.watchmakereducation.com/watches101_funamentals.htm


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## Lee1959 (Apr 1, 2006)

10 minutes per month, that is 30 seconds per day? Sounds like your automatic needs regulating if it is that inaccurate. I have 3 currently, and have had many others and none of them are/were anywhere near that bad, most are within a few seconds per day, one is about 10 seconds per day and it is the least accurate, and none of them have ever been in for regulating which would make them much more accurate.

As far as why digitals are so inacurate, well, they are so ugly they can't look to tell the correct time  . I hate digital watches, lol.


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## BobVA (Apr 1, 2006)

A good mechanical watch, properly adjusted and regulated, should be able to hit +6 to -4 sec/day (this is the COSC standard to be rated a "chronometer"). Ultra cheap mechanicals, from back in the day, might be as much as a minute off a day, which was good enough for their use and price.

Quartz watches suffer from frequency variation, primarily due to temperature, in the quartz crystal oscillator. Secondary effects due to aging and voltage changes are lesser contributers. To reduce battery drain, watches use relatively low frequency crystals, which makes the problem worse. 

Both cheap mechanicals and cheap quartz watches share a problem with repeatibility. Even if you get them "dialed in" for a given set of conditions, their rate will change with various environmental conditions.

This is relatively easy, but not cheap, to fix. High accuracy crystal oscillators are typically enclosed in a small insulated box with a heat source, called an "oven", giving the Oven Controlled Crystal Oscillator, or OXCO. The temperature in the oven is tightly controlled by a separate circuit. But these pull a relatively large amount of power and aren't suitable for battery power.

The next step down the accuracy chain is the Temperature Compensated Crystal Oscillator, or TXCO. These incorporate a temperature sensing circuit to regulate the frequency of the crystal based on a prediction of frequency change vs. temperature. Although not as accurate as an OXCO they are ahuge improvement on uncompensated, low frequency crystal oscillators and don't need much more power.

Although there are a couple of accuracy improvement schemes for quartz watches, TXCO's and higher frequency crystals are pretty much the rule now. Breitling "Superquartz" watches and Seiko "Perpetual Calendar" analog quartz watches both advertise something like +/- 20 sec/year accuracy, and I've seen them do better. If you need an extremely accurate watch, the Seikos are tough to beat on price ($200'ish) and have 10 year battery life.

"Atomic" quartz watches aren't any more accuate than regular quartz watches. Sometimes they are actually worse, since they don't need short term accuracy. What makes them so precise is that their built in WWVB receiver resets them every day to the correct time, giving the short term variability, but very high long term accuracy.

A similar thing happens with electric clocks which derive their time base from the 60Hz power line. This varies a bit in the short term, but is corrected by the power company so they have relatively high accuracy over the long term.

Cheers,
Bob


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## PhotonWrangler (Apr 1, 2006)

Had a funny discussion with a woman once about accuracy. She said "your clock must be off because it disagrees with the one on my VCR (mine was an atomic clock). Tried to explain this to her but she insisted "Oh no, I know that mine is the right time because it's DIGITAL."

Ok, whatever you say... 

Obviously "digital" doesn't necessarily mean "referenced to a stable standard or operated using a temperature-controlled crystal."

I once saw a digital time standard that used a Deuterium lamp as the time reference. I believe it operated by passing microwave or laser energy through the gas, and when the frequency of the energy hit the resonant point of the gas, the transmissivity of the gas changed slightly. A sensor at the other end measured this change and indic ated to the AFC circuit that it was on dead-center. That frequency was then measured and became the clock oscillator reference. Very cool.


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## Mike Painter (Apr 1, 2006)

Note that the original post says 12 seconds per MONTH. That's about .4 seconds per day and I suspect most do within that 12/month.
If this is a heat or vibration related cause it would mean that the plus or minus applies to the same watch which would reduce the average loss.

My new Timex is loosing about 10 seconds a month and is by far the least accurate watch I've owned for many, many years.


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## Lynx_Arc (Apr 1, 2006)

I bought my first LCD watch a long time ago... Sensor was the brand. It was accurate to less than 12 seconds..... A YEAR!.... yes.... I reset the time via shortwave WWV and in the 4 years I wore it it was never off by more than 6 seconds and I only reset it for daylights savings/losings time. I think the main reason digital watches are innaccurate is twofold.... cheap crystals and lack of factory time adjustments made to ensure more accuracy. As for temperature affecting time.... I wore the watch all year long... cold to -10 and hot to 105 F and it didn't make but a half second a month difference IMO. 
If they wanted to make more accurate digital clocks they could but they do not, instead they want to charge you $5-$20 more for some atomic radio inside and make a big deal about it. I had a casio that was off 3 minutes a month till I took it apart and turned the trim crystal or capacitor or whatever it was and it changed it to perhaps 30 seconds a month.


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## Kryosphinx (Apr 1, 2006)

I've never needed a watch to be perfectly accurate. I can't think of many reasons why perfect accuracy is necessary.
Just my 2 cents.


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## BobVA (Apr 1, 2006)

Lynx_Arc said:


> If they wanted to make more accurate digital clocks they could but they do not.



Just not the demand, I guess. Other than some niche models (like the Seiko Perpetual and the Superquartz) everybody is more interested in lower cost. I suspect Joe Watchbuyer is probably more impressed with a cooler bracelet or extra dial on his new watch than a line in the manual that says "accurate to 10 sec/yr", at least at the store.


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## warpdrive (Apr 1, 2006)

My more expensive quartz watches tend to be more accurate than my cheaper ones. My Tag Heuer Kirium quartz only lost 2 seconds over a month. My Timex Ironman was off 20 seconds over the same month (both stationary the whole time)

My mechanicals tend to vary a lot. My most accurate mechanical I've had was a Rolex. It only lost 3 seconds over a week, which is far better than other mechanicals I've owned. It was really regulated well out of the factory.


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## HighLight (Apr 1, 2006)

Kryosphinx said:


> I've never needed a watch to be perfectly accurate. I can't think of many reasons why perfect accuracy is necessary.
> Just my 2 cents.



When the missus has dinner on the table and she says you have ten seconds to get your a$$ in there.


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## sak_collector (Apr 2, 2006)

Digitals are generally accurate. The +/- 15 seconds a month is the just the spec they try to stay within, but that doesnt mean they will always be off by 15 seconds a month. I have several G-Shocks, a few may be off by up to 10 seconds a month, a couple of them stay within 2 seconds a month (without using the waveceptor) and the rest fall inbetween. Remember the +/- is a spec, not set in stone.


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## cy (Apr 2, 2006)

TSAR after 3weeks 7x24 on my wrist is +/- .7 sec off as checked against Atom time.

spec's for TSAR is .7 sec per day.


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## Metro (Apr 2, 2006)

The only reason I ever have to have perfect time is when I am having to enter the time into the computer for my GOTO telescope. I really don't see anyone having to have absolutly perfect time other than something like that. That said, I like knowing my watch is dead on. 

With atomic clocks and cell phones you are never far from the exact time, my Timex expedition that I just got last Wed has been keeping dead on perfect time for the last 4 days, I paid 40 bucks for it and it's a nice looking. 

http://store.timelinegallery.com/41301.html

It's making it hard to justify buying a new Luminox or Traser!


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## Samoan (Apr 3, 2006)

magic79 said:


> However, compared to automatics (self-wind) they are significantly more accurate. Automatics are +/- 5-10 MINUTES per month.



That sounds a bit high, really high actually. Last time I set my SMP was about a month ago. When we did the whole DST thing it was running about 30 seconds slow.

-F


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## magic79 (Apr 3, 2006)

I agree with you...I was quoting from the website.

However, quartz accuracy is a few seconds per month; mechanical is a few minutes per month.


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## tlim (Apr 3, 2006)

I've got a rolex perpetual that's gone for years, and it's not more than half a min off time every 6 mths when I check against the atomic clocks...


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## tlim (Apr 3, 2006)

Watches are very much like flashlights... You get what you pay for...  

Surefires vs. China-made lights...  




warpdrive said:


> My more expensive quartz watches tend to be more accurate than my cheaper ones. My Tag Heuer Kirium quartz only lost 2 seconds over a month. My Timex Ironman was off 20 seconds over the same month (both stationary the whole time)
> 
> My mechanicals tend to vary a lot. My most accurate mechanical I've had was a Rolex. It only lost 3 seconds over a week, which is far better than other mechanicals I've owned. It was really regulated well out of the factory.


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## Amorphous (Apr 3, 2006)

Because of DST..    

Our variable crystal oscillating time machine is off by 1 hour in 6 months (certain countries) in additional to environmental variables causing additional fluctuations.

To fix this, humankind has created a wonderful devices that instead of using vibrating quartz under voltage, aim at the SUN. ( Great activity for the young and old, and everything in between.) Here's an example:

http://www.nasa.gov/audience/forkids/activities/A_Make_a_Sundial.html



My GPS Nixie Clock is a great time reference as seen on this photo.
Thanks to the ultra-stable cesium clock reference transmitted by the ground based segments of NAVSTAR, the GPS receiver decodes and displays the time and other information on the Nixie tubes.


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## yaesumofo (Apr 4, 2006)

*Re: Why are digital watches so inaccurate?*

I know this may sound crazy but My Nixie clock which is not WWV or GPS enabled is extremely accurate. It sits just below a WWV enabled LCD clock and is never ever ever more than 1 that is ONE 1!! second off form the WWV.
I even wrote an e-mail to the company that made it to ask what they did to make it so accurate. No reply.

I have 2 quartz watches which are super accurate. A Tissot T-Touch (made in titanium) and a special edition Swatch which is a Certified Swiss Chronometer.
The chronometer in order to gain certification has to be sent to a Lab and the which is observed for accuracy under different laboratory conditions for a certain length of time. I don't know much about the process but more information is available on net, it is pretty cool.

There is a new Casio watch (also available in Ti) the PAW 1200 which is set by the WWV and It's equivalent overseas (Europe and Asia), it is also solar powered, and has a compass, temperature, barometer, waterproof....... This is one hell of a watch for something like $300.00 +-. This watch maintains super accuracy by using the WWV here in the USA. The watch itself may not be that accurate. but it sets itself daily to a very accurate source. This is cool stuff.

I am thinking that this may be my next watch in titanium.
Yaesumofo



Amorphous said:


> Because of DST..
> 
> Our variable crystal oscillating time machine is off by 1 hour in 6 months (certain countries) in additional to environmental variables causing additional fluctuations.
> 
> ...


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## cy (Apr 4, 2006)

tlim said:


> I've got a rolex perpetual that's gone for years, and it's not more than half a min off time every 6 mths when I check against the atomic clocks...


WOW... that's the most accurate I've heard from a mechanical watch. that's 5 sec per month or better than most digitals.


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## wquiles (Apr 4, 2006)

BobVA said:


> "Atomic" quartz watches aren't any more accuate than regular quartz watches. Sometimes they are actually worse, since they don't need short term accuracy. What makes them so precise is that their built in WWVB receiver resets them every day to the correct time, giving the short term variability, but very high long term accuracy.


My Casio Wave Receptor is one of these. It is solar, atomic, and a quartz watch. However, within my home office the watch can't get its 4AM re-sync signal, so I can see how the watch looses time on a daily basis - not horrible, but certainly more than I expected from a fairly modern watch. I have to move the watch and let it spend the night in the kitchen, where the signal is received with no problems.

It is obvious to me that Casio used a fairly cheap quartz movement and then count on the nightly sync in order to keep decent time. My but new-to-me (used) Traser Diving quartz watch is about 1 to 1.5 seconds fast per week, comparing to an atomic source , and it is certainly a lot more accurate than the Casio when the sync signal is not "visible" 

Will


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## leukos (Apr 4, 2006)

I have a mechanical watch that is exactly right twice a day at 11:43!


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## HighLight (Apr 4, 2006)

BobVA said:


> Just not the demand, I guess. Other than some niche models (like the Seiko Perpetual and the Superquartz) everybody is more interested in lower cost. I suspect Joe Watchbuyer is probably more impressed with a cooler bracelet or extra dial on his new watch than a line in the manual that says "accurate to 10 sec/yr", at least at the store.



Thanks for the heads up on the Seiko Perpetual lineup. I checked them out on the net and they are accurate to +/- 20 secs a year. There are loads of different models and you can get several Titanium models for under $200! They seem like an incredible bargain to me.


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## Flying Turtle (Apr 6, 2006)

Maybe I just got lucky, but my Casio Edifice model (Japanese movement) has gained but 20 sec. in over a year. Most of the time it sits on a shelf at room temp so this may help its accuracy. Other Casios in the past that got daily wear seemed to be in the 15 sec/month range.

Geoff


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## stockae92 (Apr 6, 2006)

i think for the price and purpose, Casio/Seiko/Citizen quartz watches are pretty accurate.

and if you truely desire "on the dot" timing, then there's nothing wrong with getting the "atomic" feature of Casio/Seiko/Citizen watches. i don't think that's a way to "get away with using cheap quartz" from Casio/Seiko/Citizen, but rather an "enhancement" so that you don't ever have to set your watch again (given you stay in the same time zone).

chronometer quartz is always available .. with a price tag

money can't do everything. but it can get you a very accurate watch (quartz or mechanical)


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## GadgetTravel (Apr 6, 2006)

HighLight said:


> I was browsing the Casio watch site and I noticed the specs for some watchs were like +/-12 seconds per month. Some of the more expensive watchs were a bit better. I'm wondering what makes digital watchs so inaccurate. One would think that with a digital chip and no moving parts (except for the stepper motors for the ones with actual hands) that they would be more accurate than a mechanical watch hands down. Why can't these digital watchs be more accurate, say to the tune of 5-6 seconds a month?



As a lot of other posts have pointed out, 12 seconds a month (less than 0.5 seconds per day) is actually quite accurate. One the the things that effects accuracy in both digital and mechanical watches is temperature. Mechanical watches are also effected by the positions they are in as they operate. Positions dont effect quartz watches. There is a subtype of mechanical watch made that eliminates the effect of position. It is called a tourbillon and the whole movement is inside a circular area that rotates evenly to distribute the position the parts are in during movement in an even way, hence avoiding the gravitational effects. It was invented in the late 1700s by A. L. Breguet. Tourbillons are probably still less accurate than a quartz watch and the cheapest is about $25,000. Most tourbillons go for over a hundred grand with those from the top makers (Patek, AP, Lange) being in the quarter mil to mil range depending on other features.

There is an institute in Switzerland that certifies both mechanical and quartz watch movements as "chronometers". The term dates back to the devices used to measure time by seagoing navigators. There is a book entitled "Longitude" that is a fascinating history of how watchmakers struggled to make a watch that could be used for navigation, which if I recall meant less than 5 seconds a day error. The British government put up a huge prize in the 17th or 18th century for anyone that could do it after 3 large man-o-wars returning from battling the Spaniards ran into rocks and sank as a result of faulty navigation with the loss of around 1000 sailors. Everyone from Galileo to a watchmaker in England who finally won pursued the prize. 

In chronometer testing the watche movements (not the whole thing) are run for a period of time under different temperatures and in different positions. To pass the test a mechanical watch has to lose no more than 4 seconds and gain no more than 6 per day. Requirements for quartz are much more stringent, no more than 0.2 seconds per day. 

In addition to the COSC Chronometer testing, some companies do their own. I have a Jaeger Le Coultre Master Moon. It is part of what Jeager calls their master control line of watches. Each watch is tested in different positions and different temperatures for 1000 hours straight and adjusted until it meets their performance standards or rejected. As I monitored it I think it was 1 or 2 seconds a day off (compared to a Casio atomic). I also have a Breitling Navitimer that went through the COSC testing. It came with a certificate from the COSC. It was also in the 2 second a day range. Breitling and others make COSC certified quartz watches that would be within 0.2 seconds a day. That would be about 6 seconds a month. They are probably around a grand though as a minimum price. They have something that they call a Superquartz movement that I think is even more accurate than COSC requires. Not sure if they are putting that in all of their quartz watches or not. I looked at one Superquartz last fall that was around $2000. It is probably a bit more accurate than a good Seiko or Citizen. I have a Citizen perpetual that is pretty much spot on accurate. I havent measured for a month but Im guessing it is in the 0.2 second per day range although it isnt certified.


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## Minjin (Apr 8, 2006)

My Citizen Eco Drive has been keeping very good time. Its normally about 5-7 seconds fast at DST changes.






In contrast, my trusty Timex Ironman lost about 25 seconds a month...

Mark


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## cy (Apr 8, 2006)

GadgetTravel said:


> Breitling and others make COSC certified quartz watches that would be within 0.2 seconds a day. That would be about 6 seconds a month. They are probably around a grand though as a minimum price. They have something that they call a Superquartz movement that I think is even more accurate than COSC requires. Not sure if they are putting that in all of their quartz watches or not. I looked at one Superquartz last fall that was around $2000.


my TSAR is getting .7sec for three weeks. another TSAR owner posted he was getting 12 sec per month. 

after wearing mechanical watches (submariner) for the longest time .... sure is a treat being dead on all the time.


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## Alloy Addict (Apr 9, 2006)

Minjin, that watch is beautiful!  I'd never seen that model before.


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## mchomicz (Apr 25, 2006)

GadgetTravel said:


> There is a book entitled "Longitude" that is a fascinating history of how watchmakers struggled to make a watch that could be used for navigation, which if I recall meant less than 5 seconds a day error.



GadgetTravel - thanks for pointing me in the direction of 'Longitude.' It was a great read and made me realize quite a few things all at once - not the least of which the fact that only 200 years ago there hardly was such a thing as an accurate WATCH.

Makes you kind of wonder if CASIO engineers ever feel like they are cheating with their dirt cheap yet hyper-accurate 'atomic' watches that hands down beat the best certified Swiss chronographs when it comes to accuracy - so long as they can pick up the calibration signal every night.

BTW - I recently bought such a watch (2006 model CASIO WVQ600DCA-2AV for not quite $180 from these guys - which was what originally prompted me to look around to see what ppl think about solar atomic CASIOs. I can't yet speak of the durability of the movement or life of its rechargeable battery. But I can say that CASIO must have ironed out some previous kinks in their design because my watch is able pick up calibration signal every night without requiring me to take it off for the night. I sleep with the watch on my wrist in a room that doesn't even have windows facing the direction of Fort Collins, CO (even though the manual says I should take it off for the night and put it near a window on the other side of my house - facing towards CO); I live in North Carolina.

Needless to say - I couldn't be happier with the accuracy of the watch. As someone mentioned on this forum (perhaps in another thread) I don't really NEED absolutely perfect accuracy. But I certainly can't complain if I can get it for $180 in a pretty looking package (plus whatever portion of my taxes goes to run NIST).

BTW - I'm really glad CASIO finally decided to break with their apparent tradition of putting out ugly looking (though uber-functional) watches and finally decided to start selling some more traditional looking 'timepieces' (like the WVQ600DA line or the WVQ500DBA line) Certainly made my decision to finally part with my 10-year old calculator CASIO with 10 gazzilion other functions that much easier and pick up this instead:


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