The calculation of "Phase error of impedance"

[ttcat98]

I am trying to learn to analyze raw edi data sets.
I am a little confused about the error calculation of apparent resistivity and phase. It seems that the formula for the phase error of impedance in "mtpy-v2” is incorrect.
In mtpy/core/transfer_function/z.py:

    @property
    def phase_error(self):
        """Phase error of impedance

        Uncertainty in phase (in degrees) is computed by defining a circle around
        the z vector in the complex plane. The uncertainty is the absolute angle
        between the vector to (x,y) and the vector between the origin and the
        tangent to the circle..
        """
        if self.z is not None and self.z_error is not None:
            with np.errstate(divide="ignore", invalid="ignore"):
                return np.degrees(np.arctan(self.z_error / np.abs(self.z)))

But I believe it should be arcsin instead of arctan.

[kujaku11]

@ttcat98 Thanks for the comment, looks like you are correct. Could you please attempt to fix the code with a test and create a pull request?