Hi This is my first post. OK in response...Velocity is a change in position with time. If the sensor sensed velocity, you would integrate (calculus word) the velocity time series (record of velocity with time) to get position. Acceleration is the change in velocity with time. So you would have to integrate the acceleration time series to get velocity. Hence you have to integrate a time series of acceleration twice to get position. A 2-times integration involves setting some initial conditions: ex: the object was stationary at time = 0 and the position of the object was 0 at time = 0. The last condition is easy to satisfy since we can arbitrarily set the x=0 point to anything. But the initial velocity must be known at the start of the time series. "Time series" is a time record of the velocity and/or the position of the object. The only thing that I haven't defined is "integrate". That is a term used in Calculus to indicate summing over time. A book on either Calculus or Numerical Analysis will explain how to numerically integrate. If you consult one of these books, you will find out that integration results in errors that grow with time (from t=0). The errors can be reduced by reducing the time step used in the integration, but this error is the principal drawback to using accelerometers to deduce position. I hope that this brief explanation helps...