The frequency method is an indirect method of measuring cable tension, in which using the relation between vibration frequency and cable tension, and measured frequency. It has been found wide use because of its simplicity, practicable use, higher accuracy and the instrument is easy to carry. The principle of the frequency method is based on the vibration theory of string or beam. The flexural rigidity of cable is ignored in string vibration theory, but included in beam vibration theory; therefore the latter is more approaching the engineering practice.