An apparatus for non-contact monitoring of travelling objects being produced in an unguided linear process comprising: a toroidal structure with an open aperture defining a measuring zone, a source of radiation configured by a plurality of radiation devices circumferentially disposed within the measuring zone whereby the radiation source emits rays that generate a planar screen of radiation across the object circumferentially to envelop the object, a plurality of circumferentially disposed recording devices for receiving radiation from the radiation devices following interception of the rays by the objects, and analysis means for analyzing imaging information of the emitted radiation recorded by the recording devices thereby to provide a measure of the physical characteristics of the object.