A measurement mark on a substrate has a first section with first primary and first secondary lines. The first primary lines have a first width and are arranged at a first pitch and in alternating order with the first secondary lines. A second section comprises second primary and second secondary lines arranged in alternating order. The second primary lines have a second width that is different from the first width. The pitch of the primary lines and the distance between the primary and the secondary lines is the same in each case. The spectral response of both sections of the measurement mark is determined by an analyzer unit of a measurement apparatus, and a sign of a difference between target and actual widths of the lines is determined by comparing a first spectrum derived from the first section with a second spectrum derived from the second section.