The basic function of a watch is to tell us the time, and the most basic type of watch counts the passing of hours, minutes, an usually seconds (a time only watch). But pocket and wrist watches also can have a variety of added features:
24 hour time: This type of watch not only tells the time on a 12 hour dial, but will also indicate the time in “24 hour” format. Notable models include the Hamilton 4992b (exclusively 24 hour), and the Rolex GMT (both 12 and 24 hour, can be set for two time zones).
Calendar: A calander Watch has many variations, including the day of the month; the day of the month and day of the week; the day of the month/week and the phase of the moon. A standard calander watch will have to be corrected the end of each month for the number of days in the month. To solve this issue, a highly complex variation was produced called the perpetual calander (not to be confused with the Rolex Perpetual, actually Rolex’s name for their automatic) . A notable example is the ‘Patek Philippe Perpetual calander chronograph’ originally introduced around 1941.
Automatic: The automatic watch utilizes movement from your arm and body to keep the watch wound up. Other names include ‘self winding’ watch, and Rolex’s Perpetual (not to be confused with a perpetual calander watch, see above).
Chronograph: These have a “stop watch” function. On either side of the stem there usually are buttons that operate the start/stop and reset function. Sub dials include a 30 or 45 minute counter, and a 12 or 24 hour timer.
Repeater: The Repeater complication is mostly found in antuque pocket watches, developed out of the need to tell the time in the dark. Sliding a lever will prompt the watch to ‘strike’ the hour and quarter hour increments (quarter repeater), or in 5 minute increments (5 minute repeater).
Chronometer: Watches such as Omega and Rolex come with a designation “Certified Chronometer”, or “Officially Certified Chronometer”. Modern watches that carry this designation are certified by the “Contrôle Officiel Suisse des Chronomètres” (COSC). These watches are held to a very high standard of accuracy. Various methods and governing agencies have certified antique and vintage watches in times past. Note also that the term “Chronometer” is included on dials of many lesser quality watches that are not certified at all.