HAIR SPRING, MOVEMENT, CLOCK, AND METHOD FOR MANUFACTURING HAIR SPRING

PROBLEM TO BE SOLVED: To eliminate a large bent portion in an outer end curve region R of a hair spring 1 used for the balance 19 of a clock 15 and reduce thickness.SOLUTION: The hair spring 1 has a spiral shape formed by winding a linear spring material 2. A spiral is approximately circular in a plan view viewed from a vertical direction, and a cross section in a vertical direction passing the center of the spiral is approximately W-typed. Thereby, eccentricity following expansion and contraction of the hair spring 1 is reduced, and the same rate accuracy and isochrony as a Breguet hair spring 103 are obtained. A large bent portion in a surface direction and vertical direction of the spiral in an outer end curve region R of the hair spring 1 is eliminated to reduce temporal deformation.