Subdials are the mini-dials that sit on the watch face or dial. Also known as auxiliary dials, subdials serve different functions—like tracking lapsed seconds, minutes, and hours, the phases of the moon, a second time zone —across mechanical and specialty watches like chronographs, calendars, and GMT watches.

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.

Easily one of the most beloved watch complications in the world is the melodious minute repeater. Minute Repeater watches chime the time out loud, on demand, usually by the push of a button, slide, or lever on the side of the watch. An elaborate labyrinth of mechanics, minute repeaters chime beautifully pitched sounds to signal the hour (a low-pitched note); the quarter-hour (a double note with both a high and a low pitch); and the minutes past the most recent quarter-hour (a high-pitched tone).

One of the most difficult complications to build, minute repeater watches usually house more than 300 tiny parts in their movements, including gongs and hammers to chime the time. The work that goes into building a minute repeater renders it one of the most expensive watches on the market and one of the rarer breeds. They are typically made in limited numbers and only by top haute horology brands.

While building the mechanics for a minute repeater is challenging, many watch brands agree that the more difficult feat is achieving the perfect sound (created when the hammers hit the differently tuned gongs) in terms of pitch, loudness, length and more. The number and shape of hammers used, the case and gong materials used and several other factors influence the final sound.

How Minute Repeaters Work
Minute Repeater watches house timekeeping parts, as well as the striking mechanism for the repeater, which is activated by the wearer. Additionally, there is a complex system that enables the striking mechanism to track the time to then chime the right amount of times.

Essentially, in a minute repeater, the timekeeping function operates separately from the chiming function. The repeater (which sounds when the tiny metal hammers strike the gongs) is armed via a tensioning spring or system. The wearer pushes the slide to create tension within the chiming spring. Then, as the slide is released, the hammers spring into motion, striking the gongs (thin strips of metal typically located on the perimeter of the case) to sound the time. To track (and ultimately chime) the exact time, the chiming portion of the movement uses tiny gears that work with the timekeeping portion of the watch to constantly keep in sync. They relay the exact time information to a series of racks, levers, and cams that, in turn, activate the hammers. It is all a highly orchestrated arrangement of mechanics. Generally, it takes a single watchmaker 200 to 300 hours to assemble the minute repeater movement.

The sound is achieved when each hammer hits one of the gongs and the reverberation projects the sound outwards. Most minute repeaters have two hammers and two gongs. The gongs are usually of different thicknesses or width to achieve distinct sounds. Generally, one hammer hits one gong for the hour. An opposite hammer hits the second gong to sound the minutes after the quarter-hours. For the quarter-hours, the two hammers alternate hitting the two gongs to achieve the high/low double sound that signals the quarter-hours. It should be noted that some repeater watches can have as many as five hammers and multiple gongs to create different sounds.

History and Future of Minute Repeaters
Chiming watches have their roots in the early clock towers of the 14th and 15th century that would strike on the hour, day and night. The invention of the chiming clock is widely credited to Daniel Quare, an English watchmaker who invented the quarter repeater at the end of the 17th century. Later, Thomas Tompion added a second hammer to the chiming clock to achieve differences in tones. By the 18th century, chiming clocks could be found in the homes of royalty and the wealthy and, thanks to their clear sounds, allowed them to know the time in the dark without having to light an oil lamp or candle.

In 1783, Abraham-Louis Breguet invented the gong spring and two steel blades instead of bells to do the chiming. This also allowed for further miniaturization to convert the chiming clock into a portable pocket watch. In the 19th century, the advent of electricity rendered the minute repeater was virtually useless. However the beloved sound and beauty of the minute repeater made it an enduring and coveted complication.

Today’s minute repeaters have become works of art and technical prowess. Some top watch brands work side-by-side with musical and engineering institutes to develop the perfect sound for their watches. Others still do it the old-fashioned way: by simply listening to and approving or disapproving the sound. Brands are also working to develop more advanced repeaters that chime different measures of time. Some brands pair their repeaters with other key watch complications, including automatons, perpetual calendars and tourbillon to create Grand Complications.

Because of the incredible mechanics housed inside, the minute repeater watch and its variants (including 5-minute repeaters, 10-minute repeaters and sonneries) are incredibly expensive. As such, it is a great category to keep an eye on in the vintage and second-hand market.

Perpetual calendar watches are one of the most coveted complications on the market today thanks to the wealth of information they offer the wearer and thanks to their harmoniously balanced dial designs. Essentially, a perpetual calendar displays the time and tracks and displays the day, date, month—automatically taking into account the different month lengths—and leap years. Most also display the phases of the moon, which you can find out more about here.

With the exception of a few perpetual calendar watches that will run for centuries, today’s perpetual calendar watches track the time and calendar information automatically until the year 2100, before needing a single adjustment on March 1, 2100. That necessary adjustment has nothing to do with the watch’s inability to continue tracking, but rather, is the result of a change in the Gregorian calendar. In the year 2100, the leap year that should occur will be skipped so that real time (according to the Gregorian calendar) coincides correctly with solar time.

Not all perpetual calendars offer the same indications in the same layout or format on the dial. Generally, watch brands use smaller subdials on the main dial to indicate the date, day of the week, and month. However, sometimes windows or apertures are used, and other times pointers and hands are used. A true “form follows function” concept, the ultimate design of the perpetual calendar watch dial follows the configuration of the movement.

How the Perpetual Calendar Complication Works

Considered a grand complication in watchmaking, perpetual calendar watches are incredibly complex, with many housing several hundred components in their movement. A labyrinth of gears, wheels, teeth, levers and more work together much like a basic computer program with a built-in mechanical memory of 1,461 days (four years). Essentially, the complex disk-and-lever systems are able to mechanically calculate the correct number of days in a month, whether it is composed of 28, 30 or 31 days, as well as the 29 days of February in a leap year.

Most perpetual calendar watches are designed to “think” that all months have 31 days. At the end of months with fewer days, the disk-and-lever systems mechanically inform the date wheel, which will skip through the unused dates to be in sync with the first day of the new month.

The calendar indications are synchronized using a long lever that guides the mechanical program and transmits the information to the appropriate display mechanisms, adjusting all of the watch’s other indications (day, leap year, etc.). The only real catch here is that the owner of a mechanical perpetual calendar watch must keep it wound (mechanical watch winders work beautifully for this), otherwise there is a bit of work involved in setting all of the functions to sync again.

History and Future of Perpetual Calendar Watches

Early calendar timepieces date back to the 15th century when astronomical clock towers inspired clockmakers to incorporate such features into large clocks. Throughout the ensuing centuries, as clocks developed, so did calendar functions—moving from watches that needed to be adjusted at the end of each month (complete or full calendars) to annual calendar watches that need a single adjustment annually on March 1, and to the perpetual calendar that needs no adjustment at all until 2100 and for a century at a time thereafter.

The development of the perpetual calendar system has been credited to British watchmaker Thomas Mudge, who invented the detached lever escapement in 1755 that made the perpetual calendar pocket watch possible. That watch is at the British Museum in London. The idea of the perpetual calendar watch, though, somehow went untouched for about another century. In 1853, Jules Louis Audemars created a perpetual calendar watch as a school piece that later transformed so that in 1875, when Audemars joined with Edward Piguet, the final pocket watch perpetual calendar that was unveiled featured a circular cam consisting of 48 months accounting for differences in dates. This was the true precursor of today’s perpetual calendar watches.

Many of today’s haute horology brands have patents on their perpetual calendar watches for a new system, a new way to display the information, or for added functions. Breguet has a patented In-Line Perpetual Calendar watch that has an instant year change, and IWC has developed a system to display the moon phase from both hemispheres on its Portuguese Perpetual Calendar. A handful of brands, including Jaeger-LeCoultre, Patek Philippe, IWC, and Ulysse Nardin, have even developed calendars that are accurate beyond the year 2100.

Additionally, some brands combine the complicated perpetual calendar watch with other functions, including astronomical indications such as equations of time or star constellations, chronographs, and even tourbillon escapements. While these watches are expensive, they are well worth the money, as they are complicated and will definitely hold their value. Smartwatch collectors regularly scour the second-hand or pre-loved watch market to find a good deal on a perpetual calendar watch.