AX3 Sample Frequencies Explained

Why doesnt the AX3 sample at exactly 100Hz?

The AX3 is specifically designed to capture the raw output from the on-board accelerometer. The on-board accelerometer chip is programmed with the requested sample rate but, as it is responsible for its own timing, the exact rate may vary slightly. Other devices will re-sample this at a fixed (more precisely timed) rate, but this approach can cause blocking/aliasing artifacts; something that is avoided by recording the raw data. Instead, timestamps are stored (at a high precision) and, for applications that required a fixed sample rate, this "reinterpolation" can be performed after the data is downloaded (and more accurately by a desktop computer) and it leaves the raw data intact. The latest version of the OMGUI includes an option to interpolate the file to a WAV or CSV.