A printing apparatus comprises a plurality of substantially identical modules forming a common sheet path. Each module includes an image receptor, a supply of marking material of a predetermined type, and a marking engine for creating an image of marking material on the sheet. Within each module a transport receives a sheet, moves the sheet to receive the image from the marking engine, and makes the sheet available for printing by a subsequent module in the sheet path. A sheet sensing system within each module detects a position of the sheet and uses that information to adjust the position of the image to be transferred to the sheet.