As you may already know 9-axis inertial motion sensors come with one-more absolute directional sensor, a 3-axis magnetometer which can help add accuracy to the tracking of absolute movement, but did you ever wonder which sensor is right for your application? Are you noticing big drifts in direction when using six-axis sensors? Then I would strongly encourage you to read the following article in Emotiv knowledge base on the benefits of using nine-axis sensors in those scenarios. The blog not only covers the differences between the two, it also provides crisp explanation on what kind of applications would benefit from these.