Calibre 420 was Cyma Tavannes first automatic movement. From what I can gather it was designed and built in-house by Cyma Tavannes. They had several variants; the basic being sub second then a sweep second and finally a variant with date mechanism (I have yet to work on one with date). They also made non-automatic versions for manual wind watches.
The automatic movements are fastened to a mounting plate that varies in size depending on case design.
Cyma calibre: 420 variants:
420: automatic, sub second
420KT: automatic, sweep second
424K: manual wind, sub second
425: automatic, sweep second, date
426KT: manual wind, sweep second
Cyma Tavannes calibre 420-425
- Made approximately: 1943-1954
- Made in Switzerland
- Power reserve around: 30h
- 17 Jewels
- 18000 B/A
- Lift angle 52°
- DM 19mm
- H 5.8mm
Surface finish is very fine with beveled edges. Some movement’s are rose copper plated or rhodium plated.
Top surface finish on plates: 8 Points
Surface finish on screws: 8 Points
Surface finish on ratchet and ratchet wheel: 7 Points
Movement Jeweling: 5 Points
Movement was modern for 1943, being a fairly early bumper design and all models having shock protection.
Movement design innovation (for 1943): 9 points
The Cyma calibre 420 base plate is devoid of any decoration, but still has beveled edges. The winding and setting mechanism feels nice to operate. Gear train has a good finish.
Base plate finish:6 Points
Setting and winding mechanism: 7 Points
Gear-train finish: 7 Points
Movement durability: 6 Point
A very nice feature found on a lot of Cyma centre seconds is the adjustable tension spring for the sweep second pinion. A very nice feature in my opinion.
Cyma had their own (CymaFlex) shock protection. It’s a little pice of art in itself.
Automatic device is well made and fairly robust.
Autowinder mechanism: 7 Points
Cyma calibre 420 will keep decent time when in good condition.
Accuracy: 8 points
Power reserve of 30 hours is a little on the low side
Power reserve: 6 Points
Cyma calibre 420 points summary:
Surface finish on bridges and top side of base plate: 8
Surface finish screws: 8
Surface finish on ratchet and ratchet wheel: 7
Movement Jeweling: 5
Movement innovative design for ca 1943: 9
Base plate finish: 6
Setting and winding mechanism: 7
Gear-train finish: 7
Movement durability: 6
Total bonus points: 0
Autowinder: 7
Accuracy: 8
Power reserve: 7
Grand total: 78-85
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