《墨子·62章 备穴》
在离隧道口一尺处掘进时，要倾斜着，向下打到地心，所用矛长七尺。
内去窦尺，邪凿之，上穴当心，其矛长七尺。
When digging a foot away from the tunnel entrance, it was necessary to tilt downward and dig to the bottom of the earth. The spear used was seven feet long.