A substrate having a plurality of features for use in measuring a parameter of a device manufacturing process and associated methods and apparatus. The measurement is by illumination of the features with measurement radiation from an optical apparatus and detecting a signal arising from interaction between the measurement radiation and the features. The plurality of features include first features distributed in a periodic fashion at a first pitch, and second features distributed in a periodic fashion at a second pitch, wherein the first pitch and second pitch are such that a combined pitch of the first and second features is constant irrespective of the presence of pitch walk in the plurality of features.