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Cyma 420
Automatic · 8.5‴ · Switzerland · 1943
Dimensions
24.2 mm
Height
5.80mm
Jewels
17
Power reserve
30h
Timegrapher
Beat rate
18,000bph
Frequency
2.5Hz
Reference: healthy amplitude ≈ 270–315° fully wound (>200° at 24 h); beat error ideally < 0.5 ms.
Movement
| Movement type |
Automatic
Mechanical movements fitted with an oscillating rotor that winds the mainspring through the wearer's natural motion. Invented by Abraham-Louis Perrelet around 1777 for pocket watches and adapted to the wristwatch by John Harwood in 1923, it combines traditional craftsmanship with everyday convenience.
|
|---|---|
| Winding type |
Automatic (Rotor-Driven)
Self-winding via a rotor whose motion winds the mainspring through a transmission gear train. The specific rotor configuration (central, micro, peripheral, bumper) is catalogued separately under Rotor Type. Standard on the vast majority of mechanical wristwatches since the mid-20th century.
|
| Setting type |
Stem Set (Crown Pull)
The dominant modern system: pulling the crown out to a setting position engages the hand-setting mechanism. Introduced in the late 19th century and refined into multi-position crowns (date, time, GMT). Used in virtually all modern wristwatches and most 20th-century pocket watches.
|
| Escapement type |
Swiss Lever
The undisputed standard of modern mechanical watchmaking. Through an elegant interplay between escape wheel, pallet fork, and balance, it delivers reliable impulses with the safety of 'draw' to keep the lever locked. Refined since the 18th century, it powers almost every quality mechanical wristwatch made today.
|
| Control type |
Balance Wheel
The heart of mechanical timepieces, the balance wheel is an oscillating component that, together with the hairspring, forms a harmonic oscillator regulating the gear train's pace. Its steady back-and-forth motion ensures the even release of energy from the mainspring, governing the watch's accuracy.
|
| Regulator type |
Pinned Regulator (or Index Regulator)
The most traditional regulator, consisting of a movable index pointer fitted with two curb pins (or a pin and a boot) that embrace the hairspring. Sliding the index along its scale changes the spring's active length, adjusting the rate. Simple, reliable, and easy to service, it remains the workhorse standard across countless mechanical movements.
|
| Rotor type |
Hammer (or Bumper) Rotor
An early automatic design where the rotor swings back and forth within a limited arc, striking small spring buffers at each end (hence 'bumper'). Introduced by John Harwood in 1923 and used in vintage calibres from Eterna, Felsa, JLC Futurematic, and early Rolex Oysters. Largely superseded by full-rotation rotors after 1948.
|
Specifications
| Lignes | 8.5‴ |
|---|---|
| Shape |
Round
It is the most common form that we can find.
|
| Complications |
Sub Second
A small seconds hand typically located on a sub-dial and is separate from the central hour and minute hands. Originating from early pocket watches where the main balance wheel drove the seconds hand, it offers an elegant way to track the passage of time without crowding the main display. It remains a testimony to the watch's mechanical precision and history.
|
| Hand count | 3 |
| Hand sizes | 1.05 x 0.70 / 0.15mm |
| Further measures | Mounting Diameter (Dm): 19.0mm |
Origin & References
| Manufacturer | Cyma |
|---|---|
| Country | Switzerland |
| Launch year | 1943 |
| COSC certified | No |
| Signature | ca. 1950: 191331, R.420, Cyma, Swiss, 17 Jewels, Tavannes Switzerland; Cymaflex-I
(Cyma 420KT, sweep second) |
| US import codes |
|
Notes
Remarks: 1943-1954
first Cyma automatic
mounted with mounting plates of different sizes, Fig.4: 12.5" , Do=27.8mm
family:
420: automatic, sub second
420KT: automatic, sweep second
424K: manual wind, sub second
425: automatic, sweep second, date
426KT: manual wind, sweep second
shock device only in calibres with suffix K
Other data: balance staff: U1656 stem: W1263 mainspring / battery: Zf928, 1.35 x 7.5 x 0.08 x 250mm balance staff ronda: 2280 (8,75) stem ronda: 1039 (11,5) Mainspring: 1.400 x 8.000 x 0.080 x 280.000 mm
first Cyma automatic
mounted with mounting plates of different sizes, Fig.4: 12.5" , Do=27.8mm
family:
420: automatic, sub second
420KT: automatic, sweep second
424K: manual wind, sub second
425: automatic, sweep second, date
426KT: manual wind, sweep second
shock device only in calibres with suffix K
Other data: balance staff: U1656 stem: W1263 mainspring / battery: Zf928, 1.35 x 7.5 x 0.08 x 250mm balance staff ronda: 2280 (8,75) stem ronda: 1039 (11,5) Mainspring: 1.400 x 8.000 x 0.080 x 280.000 mm
Compatible Parts
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