What is the most accurate mechanical watch?  How much
less accurate is it than a good quartz watch?

There are many claims, but I would give the edge to the Patek Philippe
10 Day Tourbillon:

"Tourbillons are tiny devices that keep a mechanical watch--one that
needs winding--from losing accuracy because of the effects of
gravity... With the 10 Day Tourbillon--which has a ten-day power
reserve--Patek is hoping for independent verification of accuracy of
less than one second a day (the official Swiss bureau usually looks
for a variation of four to six seconds)."

Fortune Magazine: Watch This
http://www.fortune.com/fortune/specials/2003/0616/watches/tourbillons.html

"Patek Phillipe, world leader in the horological industry since 1839,
joined forces with Stratford-upon-Avon-based jewellers George Pragnell
Ltd.

The highlight of the evening was the showcasing of the most accurate
mechanical watch in the world, the '10 Day Tourbillon' which will
retail at around £151,000."

This Is Stratford-Upon-Avon: Take time out for Sunday family day
http://www.thisisstratford-upon-avon.co.uk/stratford_upon_avon/archive/2003/07/10/strat_sport_general014ZM.html

Here you'll find an in-depth look at this remarkable wristwatch:

ThePurists: ?10 DAY TOURBILLON?: Patek Philippe?s latest masterpiece
http://www.thepurists.com/brandjpg/pp/sihh03/

Before the 10 Day Tourbillon came along, the titled of "most accurate
mechanical wristwatch" was claimed by Zenith, whose El Primero
movement is accurate to two seconds per day:

"Thanks to its 36,000 vibrations per hour, the El Primero movement is
the world's most accurate mechanical chronograph."

Watch Network: CHRONOMASTER XXT QUANTIEME PERPETUEL by ZENITH 
http://www.watchnetwork.com/ClassiApp/ClassiNews/News?process=view_story&NewsStoryID=87

"The famous Zenith cal 400 31 jewel El Primero Automatic Movement (the
same movement formerly used in the Rolex Daytona)... is accurate to
two seconds a day."

Watchseller: Zenith Class Sport El Primero Chronograph
http://watchseller.com/zenelprimaut.html

It is ironic that an inexpensive, mass-produced quartz watch from an
undistinguished manufacturer can beat these finely-crafted instruments
by a considerable margin. The accuracy of quartz timepieces varies
with temperature, but most quartz watches are accurate to about a half
second per day:

"In modern quartz clocks, the resonator is a tuning fork shape,
laser-trimmed or precision lapped to vibrate at 32,768 cycles per
second. In most clocks, the resonator is in a small can or flat
package, about 4mm long. Standard quality resonators of this type are
warranted to have a long-term accuracy of about 6 parts per million at
31°C, that is, a typical quartz wristwatch will gain or lose less than
a half second per day at body temperature."

Wikipedia: Quartz clock
http://en.wikipedia.org/wiki/Quartz_clock

In closing, I'd like to share a family anecdote on the subject of
wristwatch accuracy. My late father was fascinated by timepieces such
as clocks, wristwatches, even the WWV signal on shortwave radio. In
the 1960s, Bulova came out with what was advertised as the most
accurate wristwatch in the world, the Accutron. It used a tiny tuning
fork to maintain an accuracy of approximately 2 seconds per day. My
father was, of course, the first person on the block to own one of
these technological wonders. He set his new watch by tuning in WWV,
and every day he checked it obsessively for accuracy, fretting when it
gained or lost a few seconds. Exactly one month after he began his
Accutron project, he burst into the living room, crowing "It lost only
a minute in a month!" And, of course, that meant that the
manufacturer's claim of 2 seconds per day was right on target.
Jubilation abounded. I asked to see the watch. I admired its sleek
looks and marveled at the barely detectable, hypnotic humming sound
that its tuning fork made. Then I noticed something that made me burst
into laughter. Using the WWV signal, Dad had indeed set the clock to
the exact minute and second. However, he had set the hour hand
incorrectly. The watch was four hours off. Well, four hours and one
minute, to be precise. ;-)

Best regards,
pinkfreud

---

Request for Answer Clarification by bugbear-ga on 09 Feb 2004 10:45 PST

Sorry, I know this wasn't in the original question (at the
time I didn't realize quartz watches varied) but can you
also tell me the accuracy of a mediocre quartz watch-- i.e.
a timex?  Thanks!

---

Clarification of Answer by pinkfreud-ga on 09 Feb 2004 11:43 PST

When you pay more for a status-brand quartz watch, you're mostly
getting glitz. Like the pricey quartz wristwatches, your
garden-variety Timex quartz watch will probably maintain an average
accuracy of about a half-second a day, or 15 seconds a month:

"...even a $20 non-adjustable Timex is routinely within 15 seconds a
month through the lifetime of the battery."

IRBS Mailing List Archive
http://www.irbs.com/lists/navigation/0401/0068.html

"...my 6 year old Timex DataLink watch drifts about 15 seconds a month..."

FoxPop
http://www.foxpop.co.uk/Palm/timecopy.htm

"Accuracy: all watches are equal or inferior to the Timex accuracy
standard of + or - 15 seconds a month including the Rolex. Citizen and
others vary from + or - 20 seconds a month to some manufacturers at +
or - 30 seconds a month."

William Coakley
http://www.williamcoakley.com/wofolder/watchreview.htm

From the advertising copy of a very early Timex:

"A MICRO-COMPUTER KEEPS IT ACCURATE TO WITHIN 15 SECONDS A MONTH. IT
HAS AN AUTOMATIC CALENDAR. ITS QUARTZ CRYSTAL SPLITS EACH SECOND INTO
49,152 PARTS. IT'S THE TIMEX QUARTZ WATCH."

Blue Angel
http://www.blueangel.org.uk/BA/S/H/W1/16211.html

If there were 6 stars, this would get them.

Wow, thanks for the generous tip and the comment about 6 stars! It is
always a pleasure to research an interesting question from a literate
customer.

~pinkfreud

It is a popular misconception that cheap analog quartz watches are
more accurate that the best mechanical watches. At first glance
it may seem that a cheap analog quartz watch that deviates on average
0.5 seconds per day should be more accurate than one of the best
mechanical watches (e.g. Patek Philippe 10 Day Tourbillon) that
deviates on average 1 second per day.  But, the nature of the deviation
actually results in the mechanical watch being significantly more
accurate.  Here's why ... Quartz watches tend to deviate in the same
direction.  A quartz watch may run slow every day, or it may
run fast every day.  But, mechanical watches tend to deviate
more randomly, sometimes running slow, sometimes running fast.  Some
good mechanical watches from the best makers are very balanced so that
their mean deviation is close to 0 seconds - the amount of time they
run fast is cancelled by the amount of time that they run slow.  The
net deviation tends to follow roughly the mathematics of random walks:

http://mathworld.wolfram.com/RandomWalk1-Dimensional.html

Suppose:

m = amount of deviation of a mechanical watch (assuming 0 mean deviation)
    per day
q = amount of deviation of a quartz watch per day
N = number of days

then after N days for a mechanical watch the expected deviation is
roughly

Dm = (square root of N) * m / 2

and the expected deviation of the quartz watch is roughly

Dq = N * q

Now, let's calculate the expected deviation of the above quartz and
mechanical watches after half a year (183 days):

m = 1
q = 0.5
N = 183

Dm = 6.8 seconds
Dq = 91 seconds

Even if the mechanical watch deviated typically 2 seconds per day
(some less expensive Patek Philippe models do this) then

Dm = 13.5 seconds
Dq = 91 seconds

It doesn't even take half a year for the 2 second mechanical watch to
be more accurate than the 0.5 second quartz watch.  After only 4 days

Dm = 2 seconds
Dq = 2 seconds

As long as the mechanical watch is balanced, running slow as much as
running fast, it will eventually beat any quartz watch that accumulates
errors in only one direction.  In the real world, even a mechanical
watch that is balanced this way may drift in one direction slightly
due to variations caused by the person wearing it, but as long as those
deviations are less than the deviation of the quartz watch, the mechanical
watch will eventually be more accurate after enough days.

Pinkfr
It should be noted and I'm surprised it wasn't, that while technically
speaking they are essentially quartz watches, those that are
synchronized with the atomic clock in Colorado - Casio makes many -
are essentially as accurate as is the clock, i.e. accurate to within
one second every 30 million years.

So wihle not automatic a $50 Wave Ceptors is nevertheless far more
accurate than even a Patek.

Tourbillon watches are really amazing mechanical devices, especially
in wrist watch size, but the rotating balance wheel was invented for
pocket watches that spent most of their time in a vertical position
and need the tourbillon to compensate for this, whereas wristwatches  
- in use -  are in motion and different positions, so that this is not
really necessary.  I bet that a very expensive and equivalently finely
made wrist watch without a tourbillon would be just as accurate.
My grandfather?s pocket watch (pre-WW I) with a no-name work, but nice
case, was accurate to within a 2 seconds a day in 1970-80, until the
main spring broke (probably so accurate ?cause my dad was like
Pinkfreud?s (Hi!) and listened to the shortwave radio signal and
adjusted his watches.
Gregls-ga?s comment to the linked question is not inaccurate (Random
path wandering), but a quartz watch that consistently gains or loses
half a second (or 5 seconds even) per day, is as useful as a
radio-controlled watch that is ?perfectly? accurate.  If one knows the
constant deviation, one can allow for it, as did navigators for 3
centuries with their ships chronometers, that had a record of their
deviation noted in the lid.
I love the centuries? of work and craftsmanship that stands behind
mechanical watches, but quartz is better.
I thought Timex had gone out of business.  ??
Greetings!