Abstract: A quartz crystal plate (L) is used in determining the frequency of a frequency generator, and the frequency determined by said plate is variable as a function of temperature. The quartz plate constitutes the substrate for a surface acoustic wave device, e.g. a resonator or a delay line using comb transducers (1 & 2). The orientation in the quartz crystal of the plane over which the acoustic wave propagates, and the direction of propagation in said plane are defined in terms of a doubly rotated frame of reference as follows: the plate being a double rotation cutting plate defined by yxwl: .phi./.theta., one large surface of which is used for the propagation of a surface wave whose direction of propagation makes an angle .psi. with the second axis of rotation, where the first angle .phi. lies in the range 9.degree.24' to 13.degree.24', the second angle .theta. lies in the range 57.degree.24' to 61.degree.24', and the angle .psi. lies in the range 33.degree. to 37.degree..