Watchmakers develop timepieces that not just merely tell the right time. A watch may keep its owner aware of the elapsed time, remind when it's time to take kids away from kindergarten, or tell when the next leap year will come. Speaking about mechanical timepieces, a watch that performs additional functions besides timekeeping features 'complications'. For quartz watches, extra functions are called just functions.
Chronograph is one of the most popular complications. It may be simply called a stopwatch – a timer responsible for measuring elapsed time. A hand placed in the center of the dial instead of a common sweep seconds hand displays the elapsed time.
To start or stop the chronograph hand it is necessary to push a button (also called 'pusher') that is found on the side of the watch's case. There is another button for returning the hand to the starting point.
Chronograph watches often feature small dials on their faces. These are called sub-dials (counters, registers or totalizers). The sub-dials are used for displaying the elapsed minutes and on some watches elapsed hours. A lot of chronographs also have a sub-dial for displaying the seconds as the chronograph hand has substituted the seconds hand in the center of the dial.
As for the split seconds chronograph, a timepiece with this complication is able to measure at once more than one time segment or measure consecutive segments. An owner of the split seconds chronograph can time for example a few race-runners or lap times of one runner.
At the start of the race the watch's owner sets on the chronograph. When the first time segment ends, it is necessary to push another button. The chronograph hands then 'split' into two hands – the first hand stops while the second hand continues to time other runners or the next lap.
The watch's owner takes note of the time indicated by the stopped hand. After that he presses the chronograph button one more time – the stopped hand jumps forward and catches up with the moving hand.
The same happens as every runner comes to finish or each lap is completed. The hand of the split seconds chronograph is sometimes called 'rattrapante'.
A tourbillon is a rare and highly-priced complication of a mechanical timepiece. It is responsible for improving the timepiece's accuracy.
It eliminates slight timing errors that appear as a result of the fact that the balance oscillates at different speeds in different positions.
A tourbillon represents a tiny metal cage with balance and escapement set inside. The tourbillon cage constantly revolves thus preventing the balance from staying in an error-causing position.
Calendars represent one more really popular additional function. Most calendar watches sport a tiny window on the dial for displaying the date. If a watch also displays the day of the week, it is called a 'day-date' watch. A timepiece showing day, date, month is called 'full calendar'.
Most calendar watches count 31 days for each month, so it is necessary to reset them to '1' after a month with fewer than 31 days.
But there are also smart calendars that account the differences in the length of the months – these watches are called 'annual calendars' and run for the whole year with no need for resetting. The exception is only February with either 28 or 29 days - so an owner of an annual calendar watch will have to reset the date once a year – on March 1.
A timepiece with perpetual calendar accounts the length of every month even during leap years. If such a watch runs continuously, it will not be necessary to adjust it until 2100 (it will not be a leap year). A perpetual calendar may feature an indicator showing how many years have passed since the last leap year.
A calendar is not always presented through a window. It may also be featured with help of a sub-dial. The sub-dial has a hand pointing to the necessary date numeral.
A complication really highly demanded among travelers is the GMT function. GMT watches (also known as dual-time-zone watches) show both local time and the time in another time-zone.
The GMT function is often presented through an additional hour hand showing the hour in another time zone moving around a 24-hour scale on the dial.
Some watches show the second time zone with help of a digital display or a sub-dial.
World time timepieces simultaneously keep their owner aware of the time in all of the world's 24 time zones.
The bezel or dial of a world time watch features the names of 24 cities of the world – one city for every time zone.
The city-rings are rotated against a 24-hour ring to indicate the time in the corresponding time zones.
A moon-phase indicator reveals which phase the moon is in. It operates with help of a disk rotating beneath an aperture on the watch dial.
This complication is usually appreciated by romantics and lovers of aesthetics.
A repeater is an amazingly expensive complication that chimes out the time.
To hear the magic sounds all the watch's owner has to do is to push a button.
Minute-repeater watches strike the hours, quarter-hours and minutes. Each strike is characterized by special sound and frequency.