Cal. 660 is an ultra-thin automatic movement with date from Zenith. Closely related to other Zenith Elite movements, Cal. 660 lacks a seconds hand, and is thus reduced in height. The similar Cal. 661 has no date display.
Although officially listed in Zenith’s service documents, we were unable to locate any watch using Cal. 660. Indeed, apart from service manuals and repair parts, Cal. 660 is not seen.
Technical Aspects of the Zenith Elite Movement
The basic Elite movement measures 11.5 ligne (25.60 mm) diameter and most models are under 4 mm thick, despite a central automatic winding rotor and date complication. A few models used a larger main plate to move the date window outward or to support complications like a running 24 hour ring. The thinnest Elite movement is the hand-winding Cal. 650 at 2.83 mm and the thickest and most complicated is the large Cal. 687 at 6.20 mm.
Unusually, many Elite movements (apart from the 660 and 670 lines) feature small seconds at 9:00, a distinctive feature that differentiates the watches that use it. Some, however, feature central seconds, an adjustable 24 hour hand, a power reserve indicator, and other complications.
All Elite movements use an annular Glucydur balance wheel with a self-compensating balance spring and fine micrometer screw for adjustment. The automatic winding rotor is mounted on ball bearings like the ETA 2892 and originally included a tungsten carbide element for higher winding power. Most Elite movements boast 50 to 55 hours power reserve and all operate at 28,800 A/h.
Zenith Elite 650 and 660: Ultra-Thin
Cal. 661, a simple two-handed version, was one of the original Elite movements. The hand-winding Cal. 650 and 655 were soon introduced as well. All of these movements were advertised as “ultra-thin” by Zenith.