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.
Once the ball bearing rotor was proven, Eterna began working to make the movements thinner. This family is reduced in thickness from 5.9 mm to 5.55 mm for non-date versions and 5.85 mm for date. Most models have 17 jewels, though later versions have a 21 jewel option. All operate at 18,000 A/h and have 48 hours of power reserve.
This movement family includes 11.5 ligne, 12.5 ligne, 13 ligne, and 13.5 ligne variants.
Cal. 1413 one of a family of automatic movements.
All movements use suffix “U” to signify Eterna-U shock protection. Suffix “D” denotes a new 3-spoke ring balance, new hairspring stud, and new hour wheel spring.