The invention provides a stabilized frequency characteristic over a wide temperature range. A quartz resonating piece is provided such that an electrical axis of quartz corresponds to an X axis, a mechanical axis of the quartz corresponds to a Y axis, and an optical axis of the quartz corresponds to a Z axis. The quartz resonating piece includes a quartz plate having a side that is parallel to an X'axis set by clockwise rotation of the X axis around the Z axis by an angle equal to or greater than -5.0.degree. and less than -1.0.degree. or by an angle greater than +1.0.degree. and equal to or less than 15.9.degree., and another side that is parallel to a Z' axis set by clockwise rotation of the Z axis around the X' axis by an angle in a range from 34.6.degree. to 35.1.degree. inclusive; or a quartz plate having a side that is parallel to the X' axis set by clockwise rotation of the X axis around the Z axis by an angle in a range from -15.9.degree. to -5.0.degree. inclusive, and another side that is parallel to the Z' axis set by clockwise rotation of the Z axis around the X' axis by an angle in a range from 34.2.degree. to 35.3.degree. inclusive.
The balance-spring is structured by photolithography and etching in a strip pre-cut from a quartz monocrystal such that the height h of the coils form, with the crystallographic axis z, an angle .theta. for adapting the thermal behaviour of the balance-spring to that of the balance, thereby reducing the variation of rate due to temperature variations.
