HPR and Z angle misunderstanding

Hi. I want only to state if there’s some difference between heading and the angle around the z axis (relative or not)

The heading is around the z axis as well, but it is rotated of 90 degrees counter clockwise, or am i wrong ?

The thing i’m having problem is that:
If i use math coordinates to calculate angles, i will obtain z angles that ideally start from the positive X axis, not from Y. So Heading value is not exactly the Z angle.

I only want to be sure of this.

That’s correct. The heading is the angle about the Z axis, starting from the Y axis.