What is a Certified Chronometer or a Chronograph: A Guide to Mechanical Watch Terminology
January 2, 2026
Understanding the terminology used to describe antique and vintage watches is essential whether you’re identifying a family heirloom, evaluating a potential repair, or building a collection. This guide explains common watch types and terms used by collectors and watchmakers, helping you interpret descriptions, movement types, case styles, and more with confidence. Whether you’re exploring pocket watches, wristwatches, chronographs, or complicated movements, these definitions will clarify the language of horology and improve your watch knowledge.
Antique Pocket Watch Terminology
Open-Face Pocket Watch
A pocket watch without a protective cover over the dial. The winding stem and sub-seconds dial are typically at 12-o’clock (or 3-o’clock in some configurations).
Hunting Case Pocket Watch
A pocket watch with a protective outer cover on the front (and sometimes back) that flips open. This style was popular for everyday carry to protect the dial.
Railroad Grade Pocket Watch
A classification used for high-accuracy American pocket watches (Elgin, Waltham, Hamilton, Illinois). Railroad-grade watches met strict standards for accuracy, regulation, and durability.
Fusee Watch
An older pocket watch with a fusee and chain mechanism designed to deliver even torque from the mainspring to the gear train for more consistent timekeeping.
Repeater
Designers developed the repeater complication 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).
Wristwatch Types & Terminology
Time Only Watch
The primary function of a watch is to tell us the time, and the most basic type of watch counts the passing of hours, minutes, and usually seconds (a time-only watch). But pocket and wristwatches also can have a variety of added features commonly referred to as “complications”.
24 hour time—GMT
This type of watch not only tells the time on a 12-hour dial but also indicates the time in “24-hour” format. Notable models include the Hamilton 4992b (exclusively 24 hours). Rolex’s GMT and GMT II can be set for 2 and 4 time zones.
Calendar Watch
A calendar Watch has many variations, including the day of the month, the day of the month and day of the week (day-date). Some watches also include the phase of the moon on the dial. A standard calendar watch will need correction at the end of each month for the number of days in the month. Engineers designed a highly complex variation called the perpetual calendar (not to be confused with the Rolex Perpetual, actually Rolex’s name for their automatic). A notable example is the ‘Patek Philippe Perpetual calendar chronograph’ introduced initially 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 calendar watch, see above).
Chronograph
These have a “stopwatch” function. On either side of the stem, there usually are buttons that operate the start/stop and reset function. Subdials include a 30 or 45 minute counter and a 12 or 24-hour timer.
Certified Chronometer:
Watches such as Omega and Rolex come with the 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 many makers printed the term “Chronometer” on a non-certified watch simply as a marketing tool.
Moon Phase Watch
A calendar type watch that also shows date/day/month, and the lunar phase on the dial.
Additional Horological Terms
Movement/Caliber
The internal mechanical engine of a watch. “Caliber” refers to the model or configuration of the movement (e.g., Rolex Cal. 3135, ETA 2824-2, Hamilton 992).
Jewels
Synthetic rubies used as low-friction bearings in the movement. A higher jewel count (e.g., 17 jewels) often indicates additional bearings and complexity.
Complication
Any function beyond simple hours/minutes, such as chronograph, date, alarm, repeater, or moonphase.
Regulation
The process of adjusting the balance and escapement to improve accuracy.
Why Understanding Terminology Matters
Knowing watch terminology helps you:
- Identify your timepiece more accurately
- Communicate effectively with watchmakers and repair specialists
- Understand value and rarity when collecting
- Describe issues clearly during service inquiries
This vocabulary also enhances your ability to research manufacturer references, movement calibers, and historical features that define vintage and antique watches.
Initiate the Repair of your Vintage Watch
If you would like to initiate the repair of your vintage timepiece contact me directly, or visit getting started.
For additional information on watches we work on please visit these pages: Vintage Rolex repair— Vintage Breitling repair —Vintage Omega repair — Vintage Heuer repair —Bulova Repair, and Pocket Watch Repair. See my FAQ for additional information, and visit Watch Repair Case Studies.