Bisector Coordinate system:

Create a bisector coordinate system is done by selecting two axes.

The origin is the intersection of the two selected axes.

The bisector line of the two axes gives the X-axis.

The vectorial product of the two axes gives the Y-axis.

If the two axes are in different planes:

The origin will belong to the first axis at intersection of the second axis,

The computation plane of the bisector line is the one that includes the first axis and the normal is given by the vectorial product of the two axis.