Without the assistance of GPS or other positioning system, position estimates obtained by integrating linear accelerations experience unbounded error growth. Even after calibration, residual biases and axis misalignments in the accelerometer measurements will quickly grow position estimate errors. For example, Industrial-grade accelerometers, such as those built-into the VN-100, can yield errors on the order of 100 meters in just 60 seconds.
We provide a detailed explanation of the difficulties of unaided positioning here:
If measurements from an indoor positioning system are available, we can provide custom filters for an indoor INS system.