In the integral we have function 𝑎(𝑥) that considers "distortions both in the optical and recording parts of the apparatus" . In , we can find several different instrumental functions that can be convoluted with the true radiation. And the true radiation can be a convolution of different broadening mechanisms. The Voigt convolution is based on Lorentzian and Gaussian profiles because the analysis starts from a Lorentzian damping model (natural radiation) with a weight which is a Gaussian one. Different approaches exist , so that the true radiation line can be assumed different from a Lorentzian function; moreover, the weight function can be different from a pure Gaussian function.