1. A calibration method for a printer, comprising: printing one or more interference patterns on a medium using a printhead configured to print on the medium a swath having a swath height in a direction; scanning the one or more interference patterns using a scanner within the printer to produce scan data; and determining, from the scan data and the swath height, a characteristic of a roller, wherein the characteristic includes an amount of media advance, in the direction, that occurs when the roller rotates by a predetermined amount, wherein the amount of media advance is determined for a plurality of locations on the roller.