That code is who want to use of 3D accelerometer.

荷兰xsens公司的mems mti 系统的模拟输出形式数据处理。在该工作模式下，mems 陀螺输出的是三轴加速度和三轴角速度的模拟电压形式，经过数模转换后进行数据处理，得到数字的输出量-Netherlands xsens' s mems mti system output in the form of analog data processing. In this mode, mems gyro output three-axis accelerometer and three-axis

iPhone加速器相关源码,iPhone Coding Using the Accelerometer()