Ok, so I haven't increased my price on battery replacement in almost ten years, but lately I have been considering pricing certain jobs higher than that because of PITA factor.
People often ask me 'How hard is it to change a battery?' and the answer is sometimes it isn't hard at all, other times it is a nightmare.
Curved cases require special dies and presses to close the case backs and some watches, like Bering and Skagen, are difficult to work with because the whole front of the watch is glass or sapphire. 
Really cheap watches, you can close the case with your fingers, but anything decent quality requires a press, or the screw down case backs require a proper case wrench or bench mounted closer, and then there are the gaskets to condition or replace.
Touching the battery with your bare fingers can and and will shorten the battery life and depending on the person's bio magnetic field, can cause leaks. 
You know who you are, magnetic persons!
I know this sounds a bit nuts, but some people have a lot of inductance or whatever it is, as well as acidic sweat, or they smoke, or various other issues.
Anyway, the proper way to handle a cell is with finger cots, which is what we do. 
Also keep in mind, that if your watch has a realistic and serious depth rating, with a screw down crown, it is advisable to replace ALL the gaskets every two years to maintain the rating and any warranties associated therewith, IF you care about such things, OR your watch comes into contact with water on any kind of regular basis, keeping in mind also that hot water voids warranties and no one should be showering with their watch on, as I've written about elsewhere. (This advice courtesy Breitling service centre)
Certain watches also require special procedures, like Seiko Perpetual Calendars, which may need to be programmed at every battery change. A warning here:
It is EXTREMELY EASY to destroy a Seiko Perpetual Calendar while changing the battery, because the cell sits on top of a VERY thin circuit board. Even programming it with a heavy hand can puncture the circuit points. 
We also use Swiss cells, which are a lot better than your average bulk purchase no name Chinese ones, just sayin'. 
I actively discourage anyone from buying really cheap quartz watches, because more often than not, they get thrown away rather than replace their cells, and at the end of the year we see garbage bags full of non-recyclable watches going into the landfill. Sometimes these watch cases are made from highly questionable metal and are toxic.
So how hard is it to change a battery?
Depends. When in doubt, see your friendly neighbourhood watchmaker.

Peace. Out.

​R

Ok, lately there has been a considerable uptick in the number of fakes crossing my bench, maybe there are seasons for this type of thing, I dunno. Some of the following is a re-iteration of parts of posts I have made in the past, so if it sounds familiar, that's why.....
A lot of fakes are blatantly obvious, like a watch that is supposed to be a mechanical and the second hand ticks in one-second increments because it is a quartz. I see a lot of fake Rolexes like this, and they are extremely cheap and awful. (Rolex did make an OysterQuartz that is now discontinued, but it it is very distinctive looking and says Quartz on the dial)
When someone deliberately misrepresents a watch as genuine, knowing it to be a fake, well, that is obviously FRAUD, and this has happened to friends of mine and customers recently. Money lost has been in the tens of thousands.
Without calling them out by name, there is a popular auction site that advises against doing side deals, that is, transactions outside the site because the site warranty and protections do not apply. This is good advice.
Nuff said?
As I have mentioned elsewhere, there are certain brands of watches that are harder to detect as fakes. Cartier, Breitling, and others use ETA and Sellita movements, (as well as their in-house ones) with Cartier or Breitling branding on them. If you take an ETA movement and put a Cartier engraved rotor on it, it will look a LOT like the genuine article. Fortunately, a good watchmaker can spot these, as the fit and finish (among other things) will give it away.
These are usually COSC certified chronometers, and that means they are the Chronometer grade ETA movements, which few fakers will go to the trouble of using. That said, I have seen ones that did go to that trouble, and the fake was virtually indistinguishable from the genuine article. What finally gave it away was the thread pitch on a certain part of the case was incorrect.
Thread pitch, that was it.
This lead to checking the serial number, and although it was a valid number, it did not jive with the watch's purchase date nor country of purchase, SO>
Another big giveaway is the serial or model number. Most fakers will not bother to use a genuine serial number and that is the giveaway, but beware that there are some who DO.
Metallurgical composition is another tell. However, stainless steel would rarely be tested for its composition, but gold often is. Something that is gold plated, obviously will wear and look bad, and is suspect especially where it is supposed to be solid gold. 
There are also watches that rarely use COSC chronometer movements, and these are the easiest to fake. An ETA movement in the lower grades is easy to engrave with the proper markings, but there are giveaways here as well.
Engravings and laser etched markings can be faked, even on sapphire crystals, so do beware.
I don't want to get into too much detail here, it would be too useful to someone looking to make a fake. 
The short version is, buy your seller, but sometimes even that fails. When it does, there are sometimes site warranties that protect the buyer, like you-know-who.
The Authorized service centres will of course tell you if your watch is a fake, but sometimes this only comes up when the watch is getting serviced, and some years may have passed since the purchase date. A certified watchmaker can identify a fake, but recently where this broke down was, a fake was sold as a new watch, and to open the case would void the warranty, so we did not do it. Turns out that the watch was indeed a very good fake, and the movement was a dead giveaway. 
There was a solid 18K gold ladies Rolex I saw in Calgary that had avoided detection as a fake for over 40 years. Because the case was solid and tested so, and the diamonds were good quality, no one questioned the authenticity of the entire piece. This one I still wonder about, obviously it was not serviced by a qualified watchmaker, as that would have revealed its bogus-ness. Or MAYBE the guy/store that sold it managed to be the one who serviced it faithfully, knowing full well it was a fake. 
I have heard sellers try and dismiss discrepancies by claiming 'Grey market' status of their wares, and be aware that a lot of these have no warranty whatsoever, even if they are authentic. 
Generally, Authorized Dealers are the safest bet, but certainly not the cheapest. Nothing is 100%, as I have seen even dealers and other high end jewellers get caught with counterfeit watches. I saw one recently with a very well known jeweller's name on the warranty card, but even the box and papers and card were all fake, fake, fake.
If it looks like a too-good-t0-be-true deal, it probably is, as the saying goes.
Let's be careful out there.

​R

I've been getting more inquiries about this, and were seems to be some confusion as to what happens during clock service.
First of all, in the case of all mechanical clocks, they require service every 8 to 12 years. Since this NEVER happens, the clock will run for decades until metal-on-metal wear cause it to fail, sometimes spectacularly. If the power of a wound mainspring is unleashed suddenly, as is the case with a broken wheel tooth or pinion tooth/stave, the backlash can destroy the clock movement.
Basically, for a mass produced clock this is game over, unless you want to spend an absurd amount of money rebuilding a wrecked movt.
For mantel clocks, because they are mostly portable, they are dropped off and serviced at your friendly neighbourhood clockmaker.
An Overhaul entails complete disassembly and cleaning in Industry Standard solutions, as well as hand cleaning of certain components. Mainsprings are assessed for wear and loss of modulus of elasticity, and replaced when necessary. The pivots on all wheel are polished and work hardened, and the plates are bushed to restore the precise geometry needed for optimum power transfer. The clock is now re-assembled and lubricated, and test run for regulation and timing. This includes not only rate adjustments, but also beat error correction and oftentimes in weight driven clocks, we find that the weights have been modified, so they need to be restored as well.
In the case of Floor clocks or Grandfather clocks, the mechanism is picked up and taken to the machine shop for overhaul. There is no way to perform the work in situ.
This brings me to the next point, if your long case or GrandFather clock is being serviced in the home, it is NOT being overhauled, usually this falls into the 'Quick Fix' category.
So what are examples of 'Quick Fixes?'
Lubrication, which should be done every 4-6 years, can be done in situ, but the dial and hands MUST be removed, and often the mechanism must be removed from the case. If the dial and hands did NOT come off, your clock was NOT lubricated correctly.
A complete lubrication requires the removal of the dial and hands, but a partial lubrication might only entail the escapement being done. 
If the clock does not perform properly after a lubrication, it is usually the sign that severe wear and tear have made an overhaul necessary. 
Other 'Quick Fixes' include regulation, Beat Error correction, Chime adjustment, and timing and regulation. Sometimes the chains get pulled right off the sprockets or they get jammed. Humidity changes can warp clock cases and sometimes you can correct for this by re-positioning the movement in the case wherever possible. 
I've come across quite a few recently that have been absolutely butchered in situ, and I do spend a lot of time correcting previous 'repairs' by 'Unskilled Hands,' shall we say. 
Anyway, we are the custodians of these often antique time machines, and they are one of the few actual antiques that can be still used on a daily basis in this increasingly tech oriented world. 

​R

Just a quick word here about the meaning and usage of the word 'Rare' as it pertains to watches and clocks.
Everybody's favourite auction site does tend to over-use the word 'rare', if you were to go by what you read there, 99% of all mechanical watches are 'Rare', or 'Unique.'
Unique means one of a kind, and obviously, should only be used when describing exactly that. 
So what about 'Rare?'
Most companies that produced mechanical watches in the last 150 years made a LOT of them, sometimes millions per year. Depending on what country you are reading this in, what we see everyday may differ from what is common where you are. Here in North America, we didn't see a lot of Cortebert or West End, but those companies made a lot of watches. In Britain you saw a lot of Smiths watches, and I see that the prices for these are rising steadily, eclipsing most Omega vintage watches. 
Which brings me to another point.
Don't accept as gospel the inflated prices you might see online. There is a slump in antique clocks right now*, and we stay in touch with many US dealers as well, who report the same thing. Pocket watches have taken a real nose dive as well, and in general the Industry is experiencing a lull. I don't know about the brands themselves and their new product, although certain well established makers seem to have no issues.
There is a lot of competition out there, and small companies pop up all the time, kickstarting their way into the market. If you look at the specs of most of these new mechanical offerings, you will see the same old ETA movts or their Sellita equivalents, followed by Citizen driven watches, usually the 9015.
(There has been a marked drop in the quality of some ETA movts, and in the case of the Sellita SW300, which is a version of the 2892 ETA, improvements have been made.)
Until other manufactures up their production to compete with ETA, unfortunately we will continue to see a lot of this.
There are still many gems to be had, watches that are under the radar, and when these start to get their just vintage due, the prices will rise. Watch manufacturing history is pretty convoluted, but it is well worth the time to find out about makers that either didn't advertise all that well or who are now largely forgotten. The Grand Daddy of them all is Eterna, watch that one. 
So definitely read the specs, (I'm talking new watches mostly here) and don't believe everything you hear or see, especially on Auction sites. That word 'Rare' is pretty common, and that mass-produced brand name watch might not be all it's cracked up to be. 

​R

*There is a slump in retail in general, and trackers of this sort of thing I have spoken to say we have been in a recession since 2018. I would agree with this, the past two years have been abysmal. 14Sep2019

Regular readers of this sporadic writing have heard me warn of the Achilles heel of Quartz watches- Magnetic fields, along with heat and leaky batteries, but the Mechanical watch has one also.
The staff of the balance in your mechanical watch has pivots that are very small, and they are hardened. They sit in a shock-absorbing assembly designed to protect them, but a good whack can and does shear them right off. 
The most common cause of this type of damage is dropping the watch, but it can also be from striking the watch inadvertently against a door frame, for example.
Now the above describes modern watches, but the older ones were even more fragile. Lacking any type of shock system, they are very likely to be damaged by any kind of shock, and that is why you see so many pocket watches with broken staffs. The shock systems were many and varied, but the one known as Incabloc, invented in 1934 by Georges Braunschweig and Fritz Marti of Universal Escapements Ltd., is nowadays the most common. There were many types of shock systems but they didn't show up right away in watches due to the extra cost. In a lot of brands, you don't see shock systems until the late 40's, and lower end watches still didn't have it in the 50's. 
Shock protection isn't infallible- it is still possible to damage the staff's pivots, but it gives a bit of extra leeway, as the balance can actually be displaced sideways without harm to a certain degree. 
Now many of you may remember the highly entertaining 'Timex Torture Tests' of the 60's, and may be wondering why they were so tough, being strapped onto water skis and thrown off bridges and other stunts.
The answer is that the design of the staff doesn't have finely turned pivots, but is a chunky rod with conical ends, that don't really break. This means that shocks will likely destroy the gears before it has any effect on the balance. It also means an increase in friction by a huge magnitude.
This was all ok, because Timexes were designed to be throwaway items, as most were riveted together and not made to be repaired. We've all seen the horrifyingly cheap watches at the checkouts or in the airport junk stores, and these take the throwaway aspect to insane lows- unknown base metals, in some cases Cadmium, and the lowest end components possible. We accumulate hundreds of pounds of these types of watches every year, and they are not recyclable. In some instances, we have detected watches that have mildly radioactive metal used in making the cases. This points to an insane lack of quality or safety control in certain countries of origin.
But I digress.
Don't drop your watch or smack it about if you can possibly help it, especially those ultra cool vintage pieces.

​R

Ok, this is going to sound a little odd, but hear me out.
Have you ever heard the expression 'The dirt was holding it together'?
Well, turns out that is almost true in some cases, particularly with clocks.
I run into this quite a lot, a clock hasn't been serviced in many years (99.99% of the time) and sometimes it runs ok, sometimes not. Sometimes it runs quite well, and here I encounter the 'Don't fix it if it ain't broke' kind of thinking. I assure you, this does not apply to a lot of mechanical things, it is better to be proactive and do preventative maintenance.
Clocks are a collection of geared wheels that are basically transmissions. The power from the weight or mainspring is transmitted to the regulating organ, the escapement. In clocks, this can be ancre type escapements like recoil or Graham dead-beat; (There is a dizzying array of clock escapements, some are outright bizarre) but also platform escapements that can be like what you find in watches- a balance wheel with a lever or cylindre escapement (on older clocks). 
The former utilize a pendulum that swings in an arc and is mathematically matched to the gear train to give the correct frequency. If you've ever watched a long case clock pendulum of a meter or so, you might have noticed how slow it is, compared to a small table clock, with a much shorter pendulum, say less than 13 cm.
The gears have pivots on each end of the arbors which pass through the usually brass plates. When no service is done, the oil dries out and dirt accumulates on the movt. Clocks are notoriously non dustproof, and this dust will collect right were you don't want it. ESPECIALLY where  there is oil or dried oil residue. If the movt has been soaked down with oil, the dirt collects everywhere and acts as an abrasive, destroying teeth, pinion leaves, levers, plates, anything that touches or slips during the running of the clock. 
This is why you cannot oil a dirty clock. It mixes with the dirt that is already there and this sludge pools in the oil sinks of the pivots. Additional dust then adds to this. In order to clean this out, you have to fully disassemble the movt, and by doing this, you are well into overhaul territory. This is where the clockmaker encounters wear and tear, and while the clock is apart is the best time to address this, obviously.
After many years (some clocks will run for 50 years unchecked) the residue of dried up grease and oil and dirt can harden into something that looks and acts almost like stone. I kid you not. I have chipped this away from plates many times. 
Corrosion also occurs, depending on the atmosphere around the clock, smoke being the number one destroyer of mechanisms. (Clocks from places where smoking was excessive are almost always wrecked) Excessive humidity is also bad, and there was an old myth about putting a jar of kerosene or something in the bottom of a long clock case to supposedly mitigate this.
Do not do this.
The vapour does indeed get around, and it sticks to the mechanism, and will form a sticky film. 
Oil or sticky films with dirt on the teeth of brass wheels will destroy them quickly, so you do not want this. Oil belongs in oil sinks, period. And sparingly at that. (the little dish shaped indentations around the pivot holes in the plate)
When a clock gets dirty and is run for many years, say decades, the dirt and corrosion and oxidization and dried up oil residue will begin to limit what is called the endshake of the wheels. Normally the wheels are free to move slightly laterally as well as turn on their axes. Endshake is absolutely critical, but you don't want too much or too little. Too little and the train is really tight and friction will overcome the force trying to run the clock. Too much and the movement is sloppy, and in wristwatches and pocket watches, endshake is finely adjusted in chronometers to make for a really good delta in positions, which is to say, the watch will run within a very tight tolerance, no matter what its orientation in space. Up, down, sideways, you get the idea.
Generally, clocks don't move, (Carriage clocks were designed to be carried) but if dirt starts to limit the endshake, and the clock is dirty, the engagement of the wheel teeth with their adjoining pinions is kept to a narrow space, and deep ruts will be carved into the steel of the pinions. The teeth may also suffer significant wear.
When the clock is all cleaned up and endshake is restored, the wheels are freer, but will encounter the ridges of the ruts and this will interfere with the running of the clock. This is why a dirty clock will sometimes be seen to run fairly well, and if the clock is overhauled it may suddenly seem to run less well. Usually the pinions are so worn that they now cause trouble.
So what does the clockmaker do about this?
Basically, the leaves of the pinions must now be careful stoned or ground to eliminate the ridges of the ruts chewed into them over many years. This involves removing a small amount of metal, and the pinion leaf must then be polished. Preservation of the shape of the leaves is also important. 
Each pinion will have 7 or more leaves, and there will be 4-6 wheels in each train, each with its own pinion. A Chiming clock has three trains, a Striking clock has two. A single train will be found in a Time-only clock like a regulator. Each leaf will be carefully repaired and then polished. Hopefully at the end of this procedure, the pinion is still within tolerance. If not, it must be replaced, and that can be.......expensive. This means that individual pinions must be cut, and this is a specialized service that is very hard to come by. On cheaper clocks with lantern pinions, (instead of leaves, the pinion has hardened wires like staves) the wires can be replaced. One by one, and this is quite tedious as we are working with blue rod and cutting and stoning the ends.....*
Lots of work, and takes lots of time to do it. 
So what do we want to do?
Why, 'Prevent the clock from getting so messed up!' I hear you say.
Why yes, that is what we want.
There will be a quiz next week.........

*If a lantern pinion fails, that means one of the staves has worn completely through and the clock will suddenly release all its energy, shearing off teeth, bending very thick steel arbors, and basically tearing itself apart. In cases like this, the clockmaker may recommend defenestration or dropping the clock into the canal. 

I've had some questions recently regarding the operation of an automatic watch. This technology goes back to the 20's, but a self winding pocket watch was made by Breguet in 1777, the same year a similar watch was claimed by Perrelet. Further claims were made by other watchmakers of the time, not the least Le Roy, but I'm not going to delve into that here, it is a hotly contested thing, being able to say you were first. Breguet still exists as a company, as does Perrelet.
An automatic watch utilizes a weight which moves with the motion of the wearer, and was at first a pendule type, followed by various designs that included 'wig-wag' wristwatches as well as 'Bumper' type weight systems.
The most common today is the rotor, or oscillating weight type. Not all automatics are created equal, I could fill pages with the history of the variations, but for the purpose of the blog, I'm just going to describe what happens inside your modern automatic watch, especially when you bring it in for service.
Generally, during a full service or CTR, the mainspring is one of those parts that gets replaced as a rule, regardless of its appearance. (For the purposes of this blog, I am talking about modern automatic watches here, which means mid 20c to present)
As I have pointed out elsewhere, overwinding is a myth, you wind your watch until it stops, if it is a manual wind. For an automatic, the motion of the wearer and subsequently the rotor inside, is what winds the mainspring. At some point, the watch is fully wound, so now what?
Adrien Philippe (of Patek Philippe) developed a mainspring with a slipping bridle. This end is not attached to the wall of the barrel as it is with manual wind watches, it slips on the wall of the barrel against a film of braking grease.
If the wearer is so active as to make the watch wind itself completely, the spring will slip, so that no damage is done to the mechanism. These springs are usually described in watch literature as 'unbreakable', but they do break occasionally. Usually the bridle end breaks off, but sometimes the spring will break right near the centre, at the winding arbor. 
So you wear your watch, the rotor spins around, and the watch winds itself. Green technology at its finest, no batteries or capacitors to worry about. 
The automatic mainspring looks like an 'S' shape when it is uncoiled, and is a very specially engineered spring. The outer coils are curved the opposite way of the centre, placing extra friction agains the barrel wall via the bridle. 
There are no fewer than 3 different types of lubrication in the barrel of a watch, and each does its job to mitigate friction. The barrel itself is smaller than a dime in most men's watches, even smaller in ladies watches. 
So that's it- your watch gets the full treatment and the spring is now brand new, ready to keep on powering the movement. A well cared for watch can last hundreds of years. Here is the spring uncoiled, next to the arbor around which it is wound:

​

I get asked from time to time about counterfeit watches. These are really no different than counterfeit shoes, clothing, sunglasses, etc. There are some really awful counterfeits out there but there are also some that are surprisingly good quality.
I'm not going to get into any kind of judgement here, if you buy one of these knowingly, depending on what you paid for it, you might not want to cross an international border with it.
Horror stories abound.
The guy who paid 5 grand for a fake Rolex Submariner, or the lady I met in Calgary who had a solid gold Rolex that was an undetected fake for 40 years.
Rolex is not the only brand that gets faked, but it is at the top of the list. I've seen fake Seiko Tunas and Apocalypse models, but also perfectly pedestrian ones.
Sometimes I just wonder......Why?
I'd expect to see High end Seikos getting faked, but so far I have yet to encounter one. For those that may not follow Seiko that closely, you can pay over Fifty Grand for one, so they aren't just that cheap watch brand everyone knows.
The long and the short of it is, know your seller. There are a lot of fake goods online, and if the price seems too good to be true, it probably is. A Qualified watchmaker can often determine the authenticity of your watch. There are exceptions. The most common faked watches are easy to spot, but I've seen Cartier and Breitling watches that were not easily verifiable. Basically this is because these companies have models that use fairly common movements, and a highly decorated (chronometer grade) ETA with (fake) Cartier engraving looks just like a Cartier- produced highly decorated ETA with genuine Cartier engraving. Ditto with Breitling. Put either of these into a quality Stainless case with a good looking dial, and you have a high quality fake.
Keep in mind a lot of these authentic high end watches have cases and bracelets made in China.
Yeah, you heard that right.
Beginning in the late fifties, a lot of Swiss companies used cases made in China and Hong Kong. This takes advantage of the definition of 'Swiss made.' At present the term means that the watch has a Swiss movement, which was cased in Switzerland, and Final Inspection in Switzerland. The case, bracelet, crystal, etc. can be made anywhere else and often are. Very few watches are entirely Swiss made, Rolex comes the closest, with their own Gold foundry on site. Patek is another.
However, (and this is where it gets interesting) the sheer number of fakes and the public awareness of them contributes to the opposite sometimes happening. 
I was at a Cash Converters where the owner was telling me one of his junior staff took in a 'fake Rolex', gave the guy 20 bucks for it, and put it in the showcase for $100.
Aaaand- of course this time it was an authentic, 18k gold Rolex, and it was purchased a few hours later. This all happened while the boss was away, and no one would have been the wiser, except that the guy who bought the watch came back a few days later with an appraisal in his hand.
He basically waved this at the hapless store owner, and mocked him for having sold him a $20,000 watch for $100.
I don't know why he thought this was necessary, but lesson learned, suffice to say.
Pawn shops are a whole other world, you could probably make a tv show out of one..........

​R

--Just an update here. Recently a very experienced customer told me he sent a watch in to Rolex service to get it regulated, as it was running a tad fast. (Rolex Canada in Toronto, @50 St. Clair Ave W.)
Well it turns out the watch was a fake. I had a look at it after it was returned, and although great lengths were taken to make the movement look like a Rolex movement, the fit and finish was suspect, and the balance bridge was fake, not to mention the movement was not free sprung.
Cosmetically it was very good, and came with box and papers, all fake. The papers were made out with the name of a legitimate (and well known) Rolex dealer, but said dealer had nothing to do with this watch, I should add. Now I say I have never met a fake I didn't spot, but that means I looked inside. That is where the truth invariably lies. Exteriors are getting so good they are almost indistinguishable. Metallurgically they are usually different, especially in the case of Rolex's special steel alloy. 
I'd like to note here that Rolex service Toronto did a full examination of the watch and returned it to the customer. He reports that the level of customer service was excellent, and at no time did he feel that they were dismissing or talking down to him because of this. They spoke with him directly and explained all the salient points of the identification, which I am not going to get into here, so Kudos to Rolex Toronto, your customer is happy and well informed. (For anyone wondering, it looks like the customer will in all likelihood get his money back.)

​R

--And for those wondering where the watch was purchased, it was NOT from an A.D., but a very popular auction site. Nuff said? 

R

This is a question I get a lot, so for those that have wondered about this you probably have correctly assumed it has to do with the alloy.
Pure gold is soft and is not used in modern jewellery, so what we usually see are alloys containing Silver, Nickel, Copper, Zinc, Palladium, and in the case of Green gold, Cadmium. Cadmium is toxic and is no longer used, but Rose gold contains Copper, and White gold has Silver added to it. White gold also often has Rhodium plating, so you aren't even seeing the lustre of the underlying metal.
As an alloy, the metal is susceptible to reaction with environmental pollutants and off gassed chemicals from the fabric lining of the jewellery box, the glue, the wood, and any plastic. 
So this is why you open your jewellery box or watch box after many months and everything is starting to look tarnished and dull.
​

Just a word of caution about watch winders.
The reason these are sold and used, is to keep an automatic watch fully wound when it is not being worn. A lot of mechanical watch aficionados have more than one auto, whether vintage or modern, and it is just more convenient to put the watch on without having to start it up, set the date and time, etc. Especially on vintage watches that do not have quick set date functions. 
Makes sense.
However, there has been increasing evidence to support the theory that watch winders can harm your watch.
There is even a warning inside the instruction pamphlet to this effect. If you set the winder at too great a rate, the watch will be wound to full, and then the slipping bridle of the automatic mainspring will slip.
If this continues hour after hour, it causes excessive wear to the mainspring and the barrel walls. This may not be an issue immediately for a new watch, but for a vintage timepiece that already has many miles on it, it can cause hiccups. And almost right away at that.
It is critical to set the winder according to the needs of the watch.
If your watch is a type that winds in both directions, you need to set the winder accordingly. In general, these watches are more efficient in the winding department, so they don't need as many rpm. Ideally, you want the winder to fluctuate direction in this case. The Winder Manual should have guidelines to help you.
In the case of a unidirectional winding watch, like the ETA 7750, only one direction is needed on the winder, but needless to say, you need to know which direction that is. The 7750 winds clockwise when viewed from the back, so that means counterclockwise when viewed from the front. This also means that the winder, when viewed from the front, needs to go against the rotor winding direction, which would mean clockwise. Clockwise from the front is the opposite of clockwise from the back.
​Capiche?
Micro rotor watches are often less efficient in the winding department, depending on the make and model. This must also be taken into consideration when setting your winder. 
This is the only time that the term 'overwinding' has any meaning. There is no such thing as being 'overwound', but to subject an automatic winding system to excessive or constant motion will slip the mainspring constantly, causing wear. When the mainspring or barrel gets worn in an automatic, it results in 'Mainspring Creep' and will shorten power reserve and the watch may even fail to wind and maintain power properly. In a manual wind watch, you can tell when the watch is wound because the crown won't turn anymore. 
This brings me back to something I say often to my vintage watch customers. 
Vintage watches are elderly, and deserve some extra respect and careful handling. Watch winders can and will mess them up.
I consulted with a wide range of watchmakers in many areas of the Industry on this subject, and more and more this is being seen as a definite issue, especially for older watches. 
​