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 12.25 ligne and 13 ligne variants. Both are 5.75 mm thick, have 19 or 21 jewels, operate at 18,000 A/h, and have 42 hours of power reserve.
Cal. 1158 one of two similar movements.