A method is described for measuring a dimension on a substrate, wherein a target pattern is provided with a nominal characteristic dimension that repeats at a primary pitch of period P, and has a pre-determined variation orthogonal to the primary direction. A head is supported by the frame and comprises means for directly contacting, scrubbing or maintaining said surface. Accordingly, the back-end controller may keep track of promotional plays and update a voucher database that logs total values and promotional values of the vouchers. In the locked configuration of the bolt locking assembly, the first and second bolts are in an interference position with the tang so as to prevent pivotal movement of the blade.