Content screening operations are facilitated in devices that receive a content that is subject to screening obligations. The contamination barrier has a blade structure configured to trap contaminant material coming from a radiation source, a bearing structure, coupled to a static frame, configured to rotatably bear the blade structure, and an eccentric mass element displaced relative to a central axis of rotation to balance the blade structure in the bearing structure. In such situations the grid signal can be uniform over an entire sequence of images and only the payload signal need be changed before being printed on each image. The step device also includes a plurality of steps movable between collapsed and deployed configurations.