The invention relates to an apparatus for monitoring the assembly of filter tipped cigarettes. After assembly a succession of the cigarettes are advanced transversely to their length through an optical device in which at least two beams of light are transmitted across the plane of movement of the cigarettes between respective transmitters and photosensitive elements. Each beam is interrupted by each cigarette for a time depending upon the effective transverse dimension of the cigarette as seen by that beam and corresponding pulses from the photosensitive elements are summed and integrated. The output of the integrator is sampled to determine if its value lies within a predetermined range and a fault pulse for rejecting cigarette is produced if the value lies outside the predetermined range.
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