What are the Accelerometer values when we reverse the direction of iphone

Question

Hello all I am working an app that interacts with accelerometer values..

That is I need to do action when I reverse its direction (when orientation is same 1 ) , and need to stop action when I come to original direction.. how can I achieve this?

Could any one suggest the way to do it..I now have the accelerator working, but I am not getting which value is changing ..

Thanks