An overlay target on a substrate is disclosed, the overlay target including a periodic array of structures wherein every nth structure is different from the rest of the structures. The periodic array is desirably made of two interlaced gratings, one of the gratings having a different pitch from the other grating in order to create an asymmetry in the array. This asymmetry can then be measured by measuring the diffraction spectra of radiation reflected from the overlay target. Variation in the asymmetry indicates the presence of an overlay error in layers on the substrate, where overlay targets are printed on subsequent layers.