The 401G-HEAD is a part of Seiko's 4S series of spring drive movements that were released in 2004. It is a high accuracy quartz oscillator and a power regulating system which consists of a high-torque mainspring and a mechanical centrifugal governor. The 401G-HEAD is an integrated, compact design that offers superior accuracy, reliability and durability, while allowing for a thin profile, which is ideal for mid-sized and smaller timepieces. This movement features a three-point accuracy trust mechanism, a unique potential spring, and a hybrid power producing system.