Figure 1.
Vibration is measured along the orthogonal x, y and z axes or vectors (see online version for colours)
Source: Griffin et al. (2006). Graphic of seated driver downloaded from the Human Factors Research Unit website, Institute of Sound and Vibration, University of Southampton; http://resource.isvr.soton.ac.uk/HRV/VIBGUIDE/2008_11_08%20WBV_Good_practice_Guide%20v6.7h%20English.pdf. Orthogonal axes downloaded from Wikipedia http://en.wikipedia.org/wiki/File:Cartesian_coordinate_system_handedness.svg