When we talk about a watch’s accuracy, what do we really mean? Essentially, the accuracy of a watch is established by comparing it to an acknowledged standard like an atomic clock (which are the most accurate time standards known). While mechanical watches are marvelous mechanisms to be appreciated and enjoyed, they are certainly not the most accurate way to tell the time.
All mechanical (and quartz) wristwatches have degrees of differentiation in their timekeeping accuracy. Therefore, watch accuracy rates are expressed as deviations from the standard—typically stated in seconds per day. Aiming for the best possible accuracy rates is, of course, one of the major efforts of luxury watch brands, with many of them proudly announcing their standards.
Different Types of Watch Movements
Watch movements, sometimes also referred to as watch calibers, are the engines that power the timepiece. There are several different types of movements, each with their own accuracy rate expectations. The two main types of movements used in today’s luxury watches are quartz movements and mechanical movements.
A quartz movement houses a quartz crystal that vibrates at a frequency of 32,768 times per second. That frequency is then regulated via an integrated circuit to deliver one pulse per second. That is why on a quartz watch with an analog display, you will see the seconds hand “tick” once per second to its next position. A quartz movement typically gets its power from a battery; however, there are some versions that run on solar power or kinetic energy too.
A mechanical movement takes energy stored in a mainspring and transfers it through the movement via a series of gears, bridges, and other tiny mechanisms at a regulated and constant pace. This regulated energy then powers the hands and (if applicable) other functions on the dial of the watch.
A manual movement, frequently also called a hand-wound movement, is a type of mechanical movement that needs to be wound-up to operate. Turning the winding crown on a watch winds up the mainspring inside the movement.
An automatic movement, frequently also called a self-winding movement, is a type of mechanical movement that relies on motion rather than manual winding to operate. The movement’s rotor swings back and forth (when worn on a wrist or placed on a watch winder, for example) to wind up the mainspring.
Accuracy of Quartz Movements vs. Mechanical Movements
Quartz movements are far more accurate than mechanical movements, typically only losing a few seconds per month. There are also High Accuracy Quartz (HAQ) movements that negate the effects of temperature changes thanks to thermocompensation, therefore only lose around ten seconds per year.
However, despite the differences in accuracy rates, mechanical movements are significantly more appreciated in the luxury watch space (thus, more expensive) than quartz movements. Expertly engineered, mechanical movements represent centuries of mechanical mastery in horology.
What Factors Affect A Mechanical Watches’ Accuracy?
Just because a watch comes out of a manufacture with a guaranteed accuracy rating, it does not mean it will stay that way forever even if they are adjusted for a range of variables. To maintain a watch’s accuracy, it needs to undergo regular servicing for regulation, adjustments, and lubrication. There are several factors that affect a watch’s accuracy and here are some of the main ones.
Drastic temperature changes can warp many parts of the watch movements, which will then comprise its ability to keep precise time. While most modern-day luxury watch brands invest plenty of money into making movement components that are better resistant to temperature swings, it is still not a good idea to subject your watch to lengthy periods of extreme heat or cold. It is standard for high-end watches to have undergone adjustments to two temperatures: hot and cold.
Resting a watch in one stationary position for a long period can cause some accuracy issues. The effect of gravity can drag certain components of the movement, such as the hairspring, thus compromising the caliber’s timekeeping rate. Therefore, watches are typically adjusted anywhere from two to six positions to compensate for positional errors:
- Dial up
- Dial down
- Winding crown (stem) up
- Winding crown (stem) at 9 o'clock
- Winding crown (stem) at 3 o'clock
- Winding crown (stem) down at 6 o'clock
As expected, higher quality watches are adjusted for more positions compared to lower quality watches. Sometimes, people confuse a watch as having “eight adjustments” to being adjusted to eight positions—this is incorrect. A total of eight adjustments typically means adjusted to six positions and two temperatures.
Magnetic fields are all around us—from simple magnetic closures on bags to electronic devices. And magnetism can have a detrimental effect on a watch’s accuracy because it can cause individual coils to stick together, thus shortening the balance spring. If a watch becomes magnetized, the movement will likely run very fast and it will need to be demagnetized (a simple process for a watchmaker).
To check if a watch is magnetized, place a compass on a flat surface and move your watch around it. If your watch moves the compass needle, it is magnetized. Luxury watchmakers have been battling magnetism for centuries and these days, they use plenty of ferromagnetic materials in mechanical movements to boost resistance to magnetism. Make sure not to keep your watch on top of computers, next to phones, and the like for a long time to reduce the likelihood of it becoming magnetized.
What is a Chronometer?
A chronometer is the name used to describe a very precise watch that adheres to a set of standards. A Swiss-made watch can only be called a chronometer if it has received a certification from Contrôle Officiel Suisse des Chronomètre (COSC)—the institution responsible for certifying the accuracy and precision of wristwatches in Switzerland.
COSC tests each mechanical chronometer for 15 days, in 5 positions, at 2 temperatures. Quartz chronometers are tested for 13 days, in one position, at 3 different temperatures and 4 different relative humidity levels.
COSC Minimum Accuracy Requirements For Chronometer Rating
|Mechanical Movement > 20 mm||Mechanical Movement ≤ 20 mm||Quartz Movement (At 23°C/73.4°F)|
|Average Daily Rate||-4 +6 seconds/day||-5 +8 seconds/day||± 0.07 seconds/day|