From bezel to tourbillon, the key timepiece definitions you need to know…

Automatic Movement: A type of mechanical watch movement that does not require manual winding. Instead, the rotor (or part of the automatic mechanism) is pulled by gravity which effectively winds the mainspring with every movement of your hand. This is also called a self-winding movement.

Automatic Watch: A watch with a mainspring that is wound by every movement of your hand throughout the day. This type of movement is also referred to as an automatic or self-winding movement.

Bezel: The outer ring that surrounds the watch face.

Caliber: The number and letter assigned to a watch model type.

Case: The outer covering of metal that encloses the inner-workings of the watch.

Caseback: The underside of the watch case that rests on your wrist.

Chronograph: A specific type of stopwatch with a sweeping second hand that can start, stop and reset with a push of the stem. Modern watches with this feature are frequently called chronographs themselves.

Chronometer: A special designation for a precision watch that has met the rigorous accuracy standards at varying temperatures and positions set by an official institute in Switzerland.

Complication: A watch with additional non-timekeeping functions. Examples of complications include a chronograph, tourbillon, perpetual calendar.

Crown: The knob on the outside watch case that is used to set the time and date. For mechanical watches, the crown is also used to wind the watch’s mainspring. The crown may also be referred to as the stem, pin, winder or winding stem.

Dial: The watch face that displays the time. A dial can also be simply called the face.

Flyback Hand: The second hand of the chronograph that can be used to time laps or multiple competitors in a race. This flyback complication allows you to reset the time on the stopwatch without having to stop the chronograph.

Jewels: Synthetic rubies or sapphires that function as bearings inside a mechanical watch to reduce internal friction and wear and increase accuracy.

Key Set: An early style of watch that was set with a small key instead of a crown.

Mainspring: The power source of a mechanical watch made of a tightly coiled (usually steel) spring. A watch effectively stores its energy in the mainspring which slowly unwinds as the clock’s wheels turn.

Manual Wind: A watch that must be wound by hand (via the crown) every day.

Mechanical Movement: A watch movement that relies on a mainspring (and not a quartz crystal) as its power source. The mainspring can be wound by hand (manual wind) or with the wearer’s natural motion as in an automatic movement.

Moon-phase: A watch face window that displays the moon’s current phase in the sky.

Movement: The watch’s inner mechanics that collectively keep time. Two main classifications of movements are mechanical and quartz.

Perpetual Calendar: A calendar display that accounts for months with varying lengths and the leap year.

Power Reserve: The amount of energy the watch has cached until it stops running.

Power Reserve Indicator: A small gauge on the dial that measures how much longer the watch can run before needing to be wound again.

Quartz Crystal: A synthetic piece of quartz that steadily oscillates at a rate of 32.768 times per second and is used within quartz movements to power the watch.

Quartz Movement: A watch movement that uses a battery and tiny piece of synthetic quartz crystal in lieu of a mainspring. When an electric current passes through quartz, the crystal oscillates with near-perfect frequency and becomes the ideal constant to measure time against.

Rotating Bezel: A bezel (or the outer ring that surrounds the watch face) that spins to perform different functions like measuring elapsed time or calculating distance and speed.

Rotor: A flat, semi-circular piece of metal, attached to a winding mechanism, inside an automatic watch that winds the mainspring as the wearer moves throughout the day.

Screw-Lock Crown: A special crown that fully screws into the watch case to make the watch water-tight.

Skeleton Case: Also called a skeleton watch, this is a watch with a transparent case (either the front or back) to showcase the watch’s movement.

Subdial or Subsidiary Dial: Refers to the small dials on the watch face that can serve a variety of purposes including keeping track of seconds, elapsed time, moon phases or, as on calendar watches, the month, date or day of the week.

Tourbillon: Depending on the position of a watch, gravity can accelerate or slow the rotation of the watch’s wheel and alter its accuracy. The highly complicated tourbillon is a mechanical watch device designed to nullify gravity’s effects by mounting the escapement (or time-keeping element like a pendulum) and balance wheel in a rotating cage.

Winding: The operation by which the mainspring of a watch is tightened. A watch can be wound manually by turning the crown or, in the case of automatic watches, via a rotor which swings as the wearer’s arm moves throughout the day.