Cal. 835 was the first mass-produced automatic watch movement from Eterna. Introduced in 1939, it was produced in volume in the 1940s and enabled the production of waterproof and anti-magnetic automatic watches for the first time. The base movement (Cal. 845 and 905) measured 9.75 ligne in diameter but the automatic versions measured 11.75 or 12.25 ligne due to the diameter of the oscillating mass. It was a bumper automatic not a free-rotating mass like later models.
Although the automatic winding system was groundbreaking, Eterna also focused on the ease of maintenance and long life of Cal. 835. The movement was designed to allow easy replacement of anchor jewels thanks to careful construction. The barrel is equipped with a special flange that allows the spring to slip rather than breaking to avoid over-winding, a key concern for automatic winding watches at that time. The company also emphasized that the bumper movement was positioned to move easily while on the wrist.
