A statistical measure of the point source divergence-induced overlay error over the print field is derived. The assumptions of a wide-sense stationary distribution of gap error and the assumption of a symmetric distribution of overlay sites on the chip field give rise to simple expressions for the overlay error variance. The computations for overlay error are also expressed in the Fourier domain. From this formulation, it is found that these simple results hold for the zero frequency and high frequency limit of gap error in the Fourier domain, even without the assumptions of stationarity.