The X, Y and Z on the KAT are the 3 different rotations around the center of the KAT device.
The picture shows a KAT device on a flat surface. When the Kat is rotated like a knob (blue path), that is rotation along the X plane When rotated upward like lifting a book to read (red path), that is rotation along the Y plane, when rotated like turning a page, (green path) that rotation in the Z plane. (Unlike other motion capture systems, the KAT does not need to be calibrated to a fixed reference before each use. Its reference point is the placement on the body.)
The video below shows the KAT rotating in X, Y and Z planes.
https://vimeo.com/993105113/7f81c7035a?share=copy ( vimeo)