A filtering flow box for receiving a supply of plastic pellets from a bottom-unloading tower silo and removing undesirable plastic strands from the pellets before they are processed for manufacturing. The dimensions of the scene to be rendered are bounded by a rectangular volume decomposed into rectangular subvolumes. The transmission frame structure includes a sync period for transmitting a fixed length frame; an async period for transmitting a variable length frame; and a control period for transmitting a control frame storing information for discriminating between the sync period and the async period. Each clock measures its time against the raw time of the clocks with which it is in direct communication and also inputs to its filter correction data for each of these composite clocks.