Cyma Tavannes calibre: 420-426

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