(1). The transmitting and receiving transducers are respectively placed at the same height of the two sound tubes. From bottom to top, the transmitting and receiving transducers are lifted upward with the same step size (≤ 100mm) for horizontal detection. If there are any suspicious points of pile quality after leveling, leveling shall be carried out to determine the longitudinal range of abnormal parts. (2) Tilt measurement. In tilt measurement, the included angle between the center of the transmitting and receiving transducer and the horizontal plane is generally 30 ~ 40. (3) Sector measurement. Fan-shaped measurement is used when the inclination measurement range of pile top and pile bottom is limited or in order to reduce the frequency of transducer lifting. It is suggested that the textbook should prevail and BCD should be chosen as the answer. Note: JTG/T F 81-01-2004 6.3.3 and JTG/T 3512-202010.3.3 both stipulate that the measuring point spacing (that is, the step size of the transmitting and receiving transducers) shall not be greater than 250.