A non-transitory machine-readable storage medium storing instructions executable a processor is described. In some examples, the instructions cause the processor to receive object data representing an object to be manufactured by an additive manufacturing process. The object data comprises data representing a plurality of planar surfaces of the object. The object data is processed to determine, for each of the plurality of planar surfaces, an angle between the respective planar surface and a plane of a reference surface of an additive manufacturing apparatus. A manufacturing orientation of the object is selected on the basis of the angles determined for the plurality of planar surfaces and a further property of the object different to the determined angles.