Hi DAQIAN,
Thanks for posting and asking your query. The placement and orientation of Relative CS is controlled by Axis/Position.
X Axis value controls the direction in which X axis of Relative CS is oriented with respect to Global CS.
For example X-value (1,0,0) orientes X-axis of Relative CS in same direction as X-axis of Global CS, and (0,1,0) means X-axis of Relative CS aligns as Y-axis of Global CS.
Y-point in similar sense orients the Y-axis of  Relative CS to that of Global CS. For example Y-value (0,1,0) orientes Y-axis of Relative CS in same direction as Y-axis of Global CS, and (0,0,1) means Y-axis of Relative CS aligns as Z-axis of Global CS.
The X Axis and Y point works in combination and are dependent on each other. For example keeping X Axis and Y point values same (1,0,0) & (1,0,0) tool will throgh the error saying "RelativeCSParameters: X and Y vectors are parallel."
Thanks,Â