Abstract: A plant is made up of a plurality of automatic stations for the performance of an assembly process of body parts or the like with there being in the stations automatic support and blocking means for the parts to be assembled and automatic assembly means for the parts supported and blocked and comprising in the stations measurement sensors in established measurement points for measurement of geometrical magnitudes of the parts in assembly with the measurement data taken by the sensors being received by a processing unit which takes any deformations of the parts in the various stations and goes back from the detected deformations to the causes thereof in the asembly process and emits a diagnosis signal of the presumed cause.