GB/T 11345-2013标准推荐的2号试块，具有体积小、质量轻、携带方便等优点，可用于基线的设定和校准、斜探头入射点和折射角的测定。在保留2号试块的优点的基础上,对2号试块进行了改进，使其扩展到能用于且符合GB/T 11345-2013规定的灵敏度设定和校准。

The calibration block No.2, recommended by the standard of GB/T 11345-2013, has advantages of small volume, light weight and ease to carry, can be used for the setting and calibration of range/time base, and determination of probe index and angle of refraction of angle probe. On the basis of retaining the advantages of calibration block No.2, the block No.2 is improved and extended so that it can at the same time be used for the setting and calibration of sensitivity as to meet the requirements of GB/T 11345-2013.