How to calculate distance using accelerometer using iphone sdk?

What is the best way to calculate t开发者_如何学JAVAhe distance between two points/Or we can say while we walk calculate distance traveled using accelerometer? My main question is that i'm working on an application in which i need to count distance using two locations but sometimes the core locations fails to update location so at that time how do i calculate the distance traveled?

You can't even get an accurate measurement of velocity from the accelerometer, so you're definitely not going to be able to get an accurate measure of distance traveled.