====== Arnold & Son Constant Force Tourbillon ======
{{wst>image_cr|Arnold & Son|Constant Force Tourbillon}}

**Constant Force Tourbillon** is a wristwatch by [[Arnold & Son]].

Constant force is an essential element in the quest for higher precision because it is difficult regulating a consistent output, e.g. isochronal time when the power input from the [[mainspring]] is constantly changing. Imagine trying to drive a car at a consistent speed with an engine that continually varies its power output.

To maximize power consistency in the Constant Force Tourbillon, Arnold & Son began at the beginning, i.e. the mainspring [[barrel]], as this is the source of the movement's power. Instead of using just one mainspring barrel, which would produce significantly different amounts of torque between fully wound and nearly empty, the Constant Force Tourbillon has two symmetrical barrels in series, visible dial side at 10 30 and 1 30. The first mainspring barrel alone powers the [[gear train]], while the second barrel tops up the first whenever its torque output drops below optimal. This ensures that the power to the regulator flows as constantly as possible.


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**Reference:**
  * 1FCAR.B01A.C112C

**Movement:**
  * Exclusive Arnold & Son mechanical movement [[A&S5119]], hand-wound, 21,600 A/h
  * [[Tourbillon]]
  * Double [[barrel]]
  * Movement decoration [[nickel]]-silver and steel movement, [[palladium]] treated bridges and NAC grey treated main plate with [[Haute Horlogerie]] finishing hand-[[chamfered]] [[bridge]]s with polished edges and brushed surfaces, screwed gold [[chaton]]s, screws with bevelled and mirror-polished head
  * Tourbillon cage mirror-polished with hand-chamfered polished edges and circular satin-finished surfaces.
  * 39 [[jewels]]
  * 90 hours [[power reserve]]

**Case:**
  * 18 ct [[red gold]]
  * Ø 46 mm, H ? mm
  * Domed, [[antireflective]] on both sideses [[sapphire crystal]]
  * Transparent caseback in [[sapphire crystal]]
  * [[Waterproof]] to 3 atm

**Dial:**
  * Anthracite open dial

**Functions:**
  * Hours, minutes, [[dead-beat seconds]]
  * Constant force

**Bracelet:**
  * Hand-stitched brown bottier alligator leather with patina

**Limitation:**
  * 28 pieces
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{{tag>Watch_models Watches_with_tourbillon Arnold_&_Son_models}}