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Watch Accuracy

The accuracy of your watch is expressed in seconds per day. If your watch is running at +5 seconds per day, this means that each day, your watch is gaining 5 seconds. Therefore, after 12 days, your watch will be 1 minute ahead of the correct time.

Mechanical Movements

Mechanical watch movements are comprised of small gears, miniature screws and paper-thin springs. To combine all these minuscule pieces, and create a working, accurate watch is an amazing feat to begin with.

Accuracy of Mechanical Wristwatches - What to Expect

In the world of mechanics, anything assembled of small parts which are capable of maintaining 99% accuracy would be considered a top-tiered piece of machinery. To put things in perspective, if a watch is only 99.9% accurate it would be off by 1 minute and 27 seconds per day, which is acceptable in the luxury watch world.

Accuracy is dependent on a few variables, such as:

1. Position: Due to gravity a watch will gain or lose more time if laid to rest in a single position. The balance wheel has been adjusted to compensate for losses and gains in different positions. An adjusted watch should perform overall within the specification when worn throughout the day. If you remove the watch at night you may want to find the optimum position that will compensate for drift during wear.

Watches are typically adjusted to between 2 - 8 positions:
1. Dial Up
2. Crown Down
3. Dial Down
4. Crown Left
5. Crown Up
6. Crown Right
7. Half-way position crown up
8. Half-way position crown down

A watch adjust to 2 positions has been adjusted to the first 2 positions, a watch that has been adjusted to 4 positions has generally been adjusted to the above 4 positions and so on.

2. Temperature: The environment may have an impact on how accurate the watch operates. Temperature changes expand and contract many of the parts, changing the dimension and shapes - especially the balance wheel and hairspring. In modern watches most materials and designs are able to compensate for the changes and maintain a consistent rate. This is generally not a problem unless the watch is constantly in extreme weather environments and is corrected by a very simple regulation.

The standard acceptable accuracy of mechanical wristwatches is as follows:

Modern Mechanical non-COSC Certified watch
Acceptable: +/-10 seconds per day = 99.988% accuracy
Typical: +/-5 seconds per day = 99.994% accuracy
Excellent: +/-3 seconds per day = 99.996% accuracy

Modern Mechanical COSC Certified watch
Acceptable: +6/-4 seconds per day = 99.994% accuracy
Typical: +/-3 seconds per day = 99.996% accuracy
Excellent: +/-1 seconds per day = 99.998% accuracy

It is important to understand that a fresh watch off the shelf may need a break-in period of a month or so. This allows the watch to find its beat and distribute the lubricants evenly.

The warranty provided by AuthenticWatches.com covers the Swiss-manufactured movement of the timepiece. If it is determined that the timepiece is faulty due to an original manufacturing defect, the watch will be serviced under warranty.

Maintenance

Mechanical watches require periodic maintenance. Eventually a complete overhaul will be required. An overhaul is a routine movement maintenance service that cleans and lubricates the internal components of the timepiece. The movement maintenance service consists of the following steps:
  • Complete disassembly of movement (all components)
  • Ultrasonic cleanse components
  • Lubricate components
  • Reassembly of movement
  • Lubrication of movement
  • Calibration
  • Replacement of all gaskets
  • Pressure sealing of case
  • Pressure testing of case
  • Timing and function test

Overhauls are usually recommended every 2-3 years on automatic and quartz timepieces regardless of their functionality, much like an oil change or service for a car after a certain number of miles. That is why it is considered a “routine” movement maintenance service and is not covered under any warranty. When lubrication in the timepiece hardens or dries up, an overhaul is required to restore its proper functionality.

Quartz/Battery-Operated Watches

What is a Quartz watch?

Quartz timepieces use the quartz crystals to provide a very accurate resonator which gives a constant electronic signal for timekeeping purposes. Quartz crystals are piezoelectric, which means that they generate an electrical charge when mechanical pressure is applied to them. They also vibrate if an electrical charge is applied to them. The frequency of this vibration is a function of the cut and shape of the crystal. Quartz crystals can be cut at a consistent size and shape to vibrate at thousands of times per second, making them extremely stable resonators for keeping very accurate time.

Accuracy:

Modern quartz/battery operated watches are generally more consistently accurate than mechanical wristwatches. Quartz watches are typically accurate to +/-1 second per day. Unlike mechanical wristwatches, where accuracy is dependent upon a variety of factors such as gravity, tolerances and lubricants, quartz watches will keep a consistent time to whatever the original accuracy is. However certain environments may cause quartz watches to lose their accuracy such as proximity to high magnetic fields such as MRI equipment, doctors' offices with x-ray equipment, dentist offices, etc.

As most quartz watches easily outperform the COSC requirement for mechanical wristwatches, the COSC created a whole separate set of tests and standards for a quartz movement requiring the watch to stay accurate to an amazing 0.02 seconds per day.

As the cost of the COSC test is high, most companies choose not to certify their watches, as this would increase the price of the watch drastically. However, there are a few exceptions such as select Breitling quartz watches.

Following is what you can expect in terms of accuracy from quartz watches:

Modern Quartz (battery) Operated non-COSC Certified watch
Acceptable: +/-2 seconds per day = 99.997% accuracy
Typical: +/-1 seconds per day = 99.998% accuracy
Excellent: +/-0.5 seconds per day = 99.999% accuracy

Modern Quartz (battery) Operated COSC Certified watch
Typical: +/-0.02 seconds per day = 99.99998%
Excellent: +/-0.00 seconds per day = 100% accuracy

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