Grid Survey Module

A method of measuring level deviation in an automated storage and retrieval system, wherein the system comprises: a rail system comprising a first set of parallel rails arranged to guide movement of a container handling vehicle in a first direction (X) 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 (Y) which is perpendicular to the first direction (X), the first and second sets of parallel rails dividing the rail system into a plurality of grid cells, at least one container handling vehicle configured to operate on the rail system, wherein 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, a central control unit configured to receive, transmit and process data signals of the container handling vehicle and to receive and process data signals of the sensor, wherein the method comprises the steps of: arranging the container handling vehicle in a predetermined position on the grid, transmitting a data signal from the central control unit to the container handling vehicle commanding the container handling vehicle to move a distance in one direction (X, Y) along the grid, measuring at predetermined intervals, using the orientation sensor, at least one orientation parameter to produce orientation measurements that are indicative of the container handling vehicle's orientation within the three-dimensional cartesian reference system, transmitting data concerning the orientation measurements to the central control unit, and processing the orientation measurements using the central control unit in order to identify portions of the rail system that deviate from predetermined values.