Patent ID: 8246137

Claim:
An image forming apparatus, comprising: a transport roller having a radius and a circumference, the transport roller configured to move a substrate a distance along a substrate transport path; a fluid ejector unit including a plurality of nozzles arranged in an array having an array height in a direction transverse to the substrate transport path equal to or greater than the circumference of the transport roller, the fluid ejector unit configured to eject fluid through the nozzles to form a plurality of lines corresponding to actual distance reference values of substrate advancement on the substrate; and a determination unit configured to determine an offset value based on a difference between an actual distance of the substrate advancement along the substrate transport path based on at least one line of the plurality of lines and an expected distance based on an amount of movement of the transport roller; and wherein the plurality of lines allows the determination unit to determine the actual distance of substrate advancement corresponding up to at least a full rotation of the transport roller.