Unit vectors a_x, a_y and a_z for the three directions are also shown in the figure above.

The vector R from the origin to the point P(x,y,z) can be written as

The sense of the direction of the retangular coordinates follow a right hand rule. Using the right hand, if you rotate the x-axis toward the y-axis, the thumb points in the directon of the z-axis. Figure below shows the arbitrary but correct orientation of the rectangular coordinates.