A method of measuring n values of a parameter of interest (e.g., overlay) relating to a structure forming process, where n>1. The method includes performing n measurements on each of n+1 targets, each measurement performed with measurement radiation having a different wavelength and/or polarization combination and determining the n values for a parameter of interest from the n measurements of n+1 targets, each of the n values relating to the parameter of interest for a different pair of the layers. Each target includes n+1 layers, each layer including a periodic structure, the targets including at least n biased targets having at least one biased periodic structure formed with a positional bias relative to the other layers, the biased periodic structure being in at least a different one of the layers per biased target. Also disclosed is a substrate having such a target and a patterning device for forming such a target.