The Zenith El Primero caliber 4000 SC is based off the caliber 400 but has some modern upgrades including the use of Zenithium. It features a ball bearing rotor made from full tungsten with guilloche pattern. The automatic winding is in both directions.
Zenithium is an exclusive alloy made from aluminum, titanium, and niobium. The aluminum gives characteristics of lightness; titanium gives strength; niobium is for form memory. Zenith created this special shock absorbing alloy to strengthen the the chronograph bridge and balance.