>>
>>RETURN IIF( m.tnAzimuth2 > 180, m.tnAzimuth2 - 360, m.tnAzimuth2 )
>>That looks good ! Thank you. All I need to know is that if the returned value is negative I need to go anti-clockwise and vice versa.

In trigonometry, the positive direction is that in which you have to rotate the positive side of x axis to overlap with the positive side of y axis - which is counterclockwise. In asimuths, the zero is on positive side of y axis (aka north) and the positive direction is towards the positive side of x axis, i.e. clockwise. So the mathematical coordinates actually work in a right-hand direction (i.e. if you imagine a right-thread screw along the z axis, and rotate it the current system's positive direction, it comes above the plane; in left-handed systems it drills into the plane).

There are many more ways to make this more complicated :).