Dead reckoning is exactly as described in that pull quote, but the problem is that when you integrate, e.g., accelerometer readings to get velocity, you also in

Dead reckoning is exactly as described in that pull quote, but the problem is that when you integrate, e.g., accelerometer readings to get velocity, you also integrate its bias, which varies over time, and in the case of MEMS sensors will cause very significant errors. The solution described in this article significantly improves on that by using the pressure data on foot strike as an observation to estimate the IMU's biases and correct the IMU-only position and attitude. EDITED TO ADD: In many inertial navigation systems - presumably including this one - dead reckoning will still be used as a fallback in the case where corrections fail (i.e., no GPS or insufficient pressure data)