A method of controlling a manufacturing process, the method including the steps of a) providing a testing area with a periodic structure, where the periodic structure includes a series of sets of patterned features, b) illuminating the periodic structure with a light, thereby producing a non-zero order diffraction signal, c) collecting the diffraction signal to produce a test signature, d) matching the test signature with a reference signature, where the reference signature was previously produced by performing steps a), b), and c) with respect to a reference structure that is at least similar to the periodic structure, and e) controlling a manufacturing process using a control setting set associated with the matching reference signature.