Horology Zone Free Watch School
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Horology A ~ Z

Horology R
Radium A radioactive material applied to watch hands and dials to make them glow in the dark. Due to health concerns, it is banned.
Ratchet Wheel The wheel attached to the barrel arbor that winds and maintains the mainspring power in conjunction with the click.
Rattrapante Refer to Split-seconds chronograph
Regulating Pin Refer to Curb Pin
Regulation The act of altering the daily rate of the watch by means of moving the regulator (curb pins) or the adjustable masses on the balance in the case of a free-
sprung balance.

The part of the movement that alters the rate of the watch by changing the position of the curb pins and the effective length of the hairspring.


A watch or a clock with the hours and minutes (and seconds) indications separated (non coaxial).Also known as the index.

Remontoire A device that ensures a consistent amount of power is supplied to the escapement to improve the isochronism; it generally consists of a secondary power source somewhere in the power train or even on the escapement itself that is periodically rewound by the mainspring. (Remontoir is French for "rewind." )
Repassage The thorough re-examination or overhaul of a completed watch, including a verification of the rate before it leaves the factory for sale.
Repeater Refer to Minute Repeater
Resonating Ballance Wheels A set of two balances or pendulums housed within the same structure, designed to vibrate in harmony with each other. Theoretically, some of the imperfections inherent in a watch's hairspring and escapement will be experienced in opposition (if one bal ance gains time in a certain position, the other one will lose time in the same position). The balances should maintain a sympathetic vibration with each other; that is, should they deviate when disturbed, whether from shocks or positional variations, the imbalances will average out.
Retrograde Hands

Hands that jump backward and begin again when they reach their last indication.

e.g. a watch with a retrograde second hand will reach 60 on a scale, jump back to zero, and start again. In order words, the second hand moves like a windshield wiper.

Repoussé case A metal watchcase in which the design on the outside is produced using a die on the inside. The design is then finished by chasing and engraving, often to a very high degree of detail.
Reverso A watchcase that can be turned over within the frame. Although many brands, including Hamilton and Chronoswiss, have sold models, JLC developed the Reverso and still manufactures far more models than any other company.
Rhodium A hard, bright silver-white metal often used to electroplate white gold cases because of its chromelike appearance.
Rolled Gold A thin sheet of gold bonded to a base metal.

A chunk of metal that swivels on an axis and transmits winding energy to an automatic watch's mainspring.

Rose Gold Gold with a slightly reddish color caused by additional copper in the alloy. Rose gold, red gold, and pink gold are all slightly different alloys with varying amounts of copper and other constituent elements.

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