Abstract: An apparatus for deflecting a stream of spreadable particles comprises a rotatable hollow cylinder having a perforated circumferential shell through which the particles normally pass. The apparatus further comprises means for controlling the operating conditions of the cylinder whereby the particles fed to the circumferential shell of the cylinder can no longer pass therethrough, but are impelled in a different direction. The method for deflecting the particles comprises the steps of closing the passage openings of the cylinder during its rotary movement, reversing the direction of rotation of the cylinder and increasing the speed of rotation of the cylinder. The spreading operation may be monitored by positioning means for capturing the deflected particles adjacent the periphery of the spreading device. The deflected particles may then be transported by conveying means to an appropriate measuring device.