: Most XPS peaks are best described by a mix of Gaussian and Lorentzian shapes. XPSPEAK allows users to adjust the Gaussian-Lorentzian (G-L) ratio (often around 30%–80% depending on the instrument) to achieve a precise fit.

: Users can fix or vary critical parameters, including peak position (binding energy), height (intensity), full width at half maximum (FWHM), and area.