Here we break down the different purposes subdials can serve on particular watches, including the chronograph and moon phase.

Chronograph Subdials

The most common subdials are found on chronograph watches. In the most basic terms, a chronograph is a stopwatch. By pressing the pushers on either side of the watch case, the wearer can activate the chronograph seconds hand or stop watch functionality.

A chronograph’s subdials are sometimes referred to as “registers” that keep track of the total elapsed minutes and hours timed with the chronograph. Another subdial also measures the seconds, down to 1/10th of a second for added accuracy.

The subdials are meant to improve the overall readability of the measured elapsed time by breaking down the seconds, minutes, and hours separately. By adding up the figures you read in the subdial, you can calculate how much time as passed since you started the chronograph.

Power Reserve Indicator Subdial

Some mechanical watches (which rely on a mainspring to power the watch) will have a subdial that reads out how much stored energy the watch has left before it stops running.

GMT Subdial

Popularized during the 1950s when commercial air travel was a growing mode of transportation, GMT watches allow you to keep track of a second time zone. Typically, the second time zone is set and read via a rotating GMT bezel and a GMT hand. However, select GMT watches will actually feature a GMT subdial were the second time is displayed instead.

Moon Phase Subdial

Unlike the other subdials on the list which feature numbers, the moon phase subdial features a depiction of the moon through an aperture (or window) that tracks the phase of the moon (i.e. new, waxing, crescent, full, etc.)

Day of the Week Subdial

Another less traditionally thought of but still classified as a subdial is the day of the week subdial. Similar to the moon phase, the day of the week appears through an aperture on the main dial and reads out the respective day. One watch model that prominently features a day of the week subdial is the Rolex Day Date.

In timepieces, having a “complicated” watch is a good thing. Generally, any function other than indicating the hours, minutes and seconds on a watch is considered a complication. While multi-time zones, alarms, and other small complications are becoming very popular today, there are a handful of traditional watchmaking complications considered to be the “true classic complications” by the greater watch collecting community. Here, we take a look at these top six true watch complications that collectors are clamoring for.

1. Acoustical Watches

Just as their name suggests, acoustical watches are those that chime the time via a series of hammers and gongs. Some offer the chiming on demand, such as the minute repeater, five-minute repeater, decimal (or 10-minute repeater), quarter repeater. Others, such as grand and petite sonneries, strike the time on the hour and typically have a “silent” button.

2. Chronographs

Chronographs are essentially stopwatches. Simple chronographs that can start, stop, and reset via the pushers and flyback chronographs that offer a rapid reset feature, and split-second (Rattrapante) chronographs to simultaneously time multiple events are all considered a classic complication. The chronograph enables the measurement of these intervals of time without affecting the hour, minute, and seconds timekeeping function.

3. Perpetual Calendars

Perpetual calendars track and display all aspects of time, including day, date, month, and even the Leap Year. Most also offer moon phase indications. They take into account short months and Leap Years. Most remain accurate without needing an adjustment (unless they run out of power) until the year 2100, when we will skip a scheduled Leap Year.

4. Equation of Time

The most complex astronomical watches are ones that display the Equation of Time. Obviously, all watches track the 24 hours in a day. However, the true solar time of a day varies by as much as 16 minutes longer or 14 minutes shorter than 24 hours. The Equation of Time watch tracks the exact solar length of each day and often shows the difference between true solar time and mean solar time (or “clock time”).

5. Tourbillon

The tourbillon escapement, invented by Louis-Abraham Breguet in the early 1800s, is a constantly whirling device built into a watch to compensate for the errors in timekeeping caused by the effects of gravity pulling on a watch is in different positions on the wrist. Essentially, the tourbillon escapement keeps the timekeeping as precise as possible.

Today’s watch pundits and experts argue as to whether or not the tourbillon is a true complication. On the one hand, the tourbillon offers an added feature by keeping more accurate time. On the other hand, as today’s watches have become much more accurate in general, some argue it is a superfluous addition to a watch, offering only added complexity and beauty. Today’s tourbillon escapements have become ever more complex with multiple axis tourbillons, double-, triple- and even quadruple-escapements. As such, the Tourbillon remains a classic complication.

6. Ultra-Thin Watches

Again, more of a feat of craftsmanship than an added function, ultra-thin watches are among the most difficult to create and are true works of art. In an ultra-thin watch, all of the watchmaking components are pared down to make a timepiece so slim that, in some instances, the watch is the thickness of a half dollar coin. The incredible watchmaking expertise that goes into creating extra-slim movements keeps this realm on the classic complication list.

It should be noted that when a watch brand combines multiple (usually at least three) classic complications from the list above into a single timepiece, it becomes a Grand Complication. Learn more about the fascinating world of Grand Complications in our blog post here!

Ever gaze at someone’s watch and see the moon? If so, you are witnessing a small complication in watchmaking that is one of the most beloved on the market: moon phase indications.

What is a Moon Phase Watch Complication?

Essentially, a moon phase complication depicts exactly what it says: it shows the phases of the moon in real time so that at any given point the current phase of the moon in the sky is depicted precisely on the wrist. Depending on the timepiece and its movement complexity, the moon phase indication is accurate to varying lengths of time (including up to thousands of years) and can display constellations and other information, as well as the phases of the moon.

Today’s moon phase watches can be simple or incredibly elaborate, depending on the brand. Additionally, the placement of the moon phase aperture and the shape of the aperture on the dial vary greatly depending on the brand. Some moon phase indications are made using precious stones such as lapis lazuli or glass aventurine. Others feature yellow or white gold moons that are sculpted, and yet others are meticulously hand-painted for visual depth and beauty.

How the Moon Phase Complication Works

While every watch brand has its own way to depict the moon’s waxing and waning, most moon phase complications operate via a small disk within the mechanics of the watch. The disk is typically painted or engraved with two identical moons on it, as well as with the phases of the moon (new moon, first quarter, full moon and last quarter). An open aperture on the dial reveals the correct portion of the moon phase disk that coincides with the night sky. For a simple moon phase watch, a 59-tooth gear that advances by one notch every 24 hours drives the moon disk. This way, the moon on the disk passes through the aperture every 29.5 days.

Generally, the most simple moon phase displays, if worn regularly, show a one-day discrepancy in the alignment of the actual moon phase in the sky and the coordinating moon phase complication in the watch every two and a half years. This is predominantly because the typical moon phase cycle is 29 days, 12 hours, 44 minutes and 2.8 seconds. In simpler moon phase watches, this time is condensed into an average of 29.5 days. Thus, within a few years, the accuracy is affected, and the wearer needs to adjust the moon phase indication. There are more advanced moon phase disks that are built using a 135-tooth wheel in order to achieve accuracy for 122 years.

Accuracy and Elegance

A handful or two of haute horology brands strive to stretch that accuracy to a mind-boggling number of years. The Richard Lange Perpetual Calendar Terraluna watch from A. Lange & Sohne, for instance, was five years in the making and offers a constantly moving moon phase display that will not need a single day’s correction for 1,058 years. Jaeger-LeCoultre’s Duomètre Sphérotourbillon Moon watch is designed to remain accurate for a full 3,887 years thanks to a complex movement system. There is even a watch created by independent watchmaker Andreas Strehler that is said to be accurate for 2 million years.

These examples, though, are not the norm. They are the exception. Most of today’s simple moon phase watches are accurate to a few years, and certain higher-tiered brands offer accuracy for up to 122 years. This year alone, brands such as Cartier, Rolex, Vacheron Constantin, Patek Philippe, Hermes, Frederique Constant, Raymond Weil and more unveiled beautiful moon phase watches that are accurate for differing periods of time and that showcase the beauty of the moon’s phases in a variety of designs.

After all, for most watch lovers, the accuracy of the moon phase is not the lure. Instead, the sublime beauty, complete with the notions of mystery and romance that the moon conjures, is the true heart grabber.

History and Future of Moon Phase Complications

Since the dawn of time, the moon has governed not just the tides, but also planting and harvesting seasons, and so much more. It has been an inexhaustible symbol of mystery and romance. Even in the early days of clock making centuries ago, master clockmakers found a way to incorporate the phases of the moon into large clocks. This concept later miniaturized and found its way to travel clocks, pocket watches and eventually wristwatches of the 20th century.

Today’s watch brands understand that consumers want something visually alluring on the wrist, and they are making strides to unveil moon phase watches for men and women, and in price ranges across the board. Additionally, many are equipping moon phase watches with other complications such as calendars with the day, date, month, leap year, and even astronomical information such as the equation of time scales (to measure the difference between real and mean solar time), northern and/or southern hemisphere constellations, and more. Some brands are even beginning to create three-dimensional depictions of the moon’s phases that are bold and daring renditions of art, elegance, and technology.