The Seiko 4206B watch movement, produced from 1953 to 1955, features a patented double-excenter winding system with jewelled rollers and a jewel-bearing rotor. Designed with an intermediate wheel to support a large balance and maintain a low profile, the movement can accommodate either a centered seconds wheel or a sub-second configuration without the need for extensive modifications. Early samples were found to have a concealed balance cock, while later samples incorporated a new rotor lock and ring balance. Notably, the movement offers automatic winding and sub-second functionality.