Abstract: A method of measuring level deviation in an automated storage and retrieval system, wherein the system includes rail system, at least one container handling vehicle, and a central control unit. The rail system includes a first set of parallel rails arranged to guide movement of a container handling vehicle in a first direction across the top of a frame structure, and a second set of parallel rails arranged perpendicular to the first set of rails to guide movement of the container handling vehicle in a second direction which is perpendicular to the first direction. The first and second sets of parallel rails divide the rail system into a plurality of grid cells. The at least one container handling vehicle is configured to operate on the rail system. The at least one container handling vehicle is provided with at least one orientation sensor configured to measure at least one orientation parameter of the sensor in a three-dimensional cartesian reference system.