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Horology A ~ Z

Horology B
Back Winder Flat crown set into the back of the case for setting time and winding.
Baguette Rectangular movement, with a length at least 3 times its width. This is a popular shape for Art Deco watches.
Balance / Balance Wheel

The equivalent of a pendulum of a clock in a watch. The balance vibrates back and forth (similar to a pendulum); the vibration produced is determined by the size and weight of the balance combined with the strength and length of the balance spring. The balance, vibrating at a set frequency, controls the watch's timekeeping.

The Balance does not rely on gravity as the restoring force, it uses a spiral-shaped spring --- balance spring.

Balance Spring

Balance spring is a very thin, spiral-shaped spring which makes the balance swinging back-and-forth and dividing time into equal parts. Each back-and-forth movement of the balance is an oscillation. 1 oscillation is composed of 2 vibrations.

In modern watches, the rate of the balance wheel is between 18,000 and 36,000 vibrations per hour (VPH).

Ball Bearing A bearing that employs stainless steel balls rolling in an enclosed space to reduce friction. Usually found on the rotor of automatic watches, some companies have begun using ceramic ball-bearings; theoretically they are a longer lasting, more efficient alternative.

Refer to Spring Bar

Barrel The watch's power source, and the mechanical equivalent of a battery. The barrel has a large coiled spring that can be wound to transmit the driving force to the power train.
Baton Numerals Undecorated non-numerical markers of hours, minutes and seconds.
Beat Rate The frequency of oscillation of the movement, usually expressed as vibrations (ticks) per hour (VPH) or as a proper frequency in hertz (Hz). Beat error is the symmetry of the "tick" and the "tock" in a mechanical movement; if the vibrations of the balance are perfectly equal in both directions, it is said to be in beat, i.e., it has no beat error.
Bezel The ring around a watch's crystal that sometimes holds the crystal in place and sometimes is merely decorative. Bezels are usually static, but can also be rotated to make mathematical calculations or keep track of elapsed time.
Bi-directional Winding An automatic mechanism that winds the mainspring with the rotor spinning in both the clockwise and counterclockwise directions.
Big Date An oversize date display, typically made up of two overlapping discs for the different digits.
Blued hands / screws Bluing steel parts is an old craft tradition which requires experience and dexterity. How to blue ?
Bombe French for "convex." A round, or domed, shape. Sometimes used to describe a specific, bulbous lug shape, i.e., bombe lugs.
Bracelet A metal watchband, usually in steel or gold.
Breguet Hands They feature a straight or slightly leaf-shaped shaft with a small circle and a slightly off-center cutout and a pointed tip.
Breguet Numerals Numbers designed in the style of Abraham-Louis Breguet.
Breguet Overcoil Refer to Overcoil Hairspring
Bridge The structure in a watch that usually supports any part of the movement and is secured on two sides; the framework of the watch.
Bubble Back Early Rolex cases with backs shaped in the form of a slight bubble.
Bumper Wind An early version of a modern automatic watch in which the rotor, or the oscillating weight, does not rotate a full 360 degrees but only a portion of that. It some times has springs at the end attached to the rotor or the frame; when it winds it bumps back and forth between the two springs.
Butterfly Clasp A watch bracelet or band in which the two ends of the buckle fold over into the center.

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