Android 传感器中，压力传感器（感应手指的触摸压力，非气压传感器）的实现问题

Question

关于Android是否可以获取触摸压力，SDK中有这样一段话支持这个观点：
“For example, when the user first touches the screen, the system delivers a touch event to the appropriate View with the action code ACTION_DOWN and a set of axis values that include the X and Y coordinates of the touch and information about the pressure, size and orientation of the contact area.”
其中
1、MotionEvent.getPressure():“Returns the current pressure of this event for the given pointer index”
2、MotionEvent.getSize()：“Returns a scaled value of the approximate size for the given pointer index”
受有道云笔记手写功能启发，请问有压力传感器开发经验的同行具体实现中主要用哪个函数？该怎么用？精确率如何？
参考：http://docs.huihoo.com/android/4.2/reference/android/view/MotionEvent.html#AXIS_PRESSURE