Power Spectral Density (PSD) analysis helps understand line-edge and linewidth roughness in lithography. Uncertainty in measured PSD makes interpretation tricky. This work used simulations to study data window functions and detrending effects on PSD measurement. The Welch window was found to be the best choice. Linear detrending leads to underestimation of low-frequency PSD. Measuring multiple edges per SEM image helps reduce this bias.