ETA was one of the three firms “chosen” to develop advanced automatic watch movements by Ebauches SA, thanks in part to their history with Eterna. The chief designer at ETA, Heinrich Stamm, had created many of the company's important watch movements, and was famous for the Eterna-Matic line of watches.
This movement family includes 11.75 ligne, 12.25 ligne, and 13 ligne variants. Those with sub seconds are 5.4 mm thick, while those with sweep seconds are 5.55 mm thick. All have 17, 19, or 21 jewels, operate at 18,000 A/h, and have 38 hours of power reserve.
Cal. 833 one of a family of similar movements.