Abstract: The cavity tracking system employs a tracking station adjacent a screw feed with closely spaced sensors which operate on a first-in first-out memory manner. When a container passes the first sensor the actual encoder "count" obtained at that time is compared with the list of cavity numbers and associated calculated "counts" in the store and the cavity number associated with the actual count is fed to the first memory zone. When the container passes the second sensor, the cavity number is erased from the first zone and passed on to the next zone and so on. Upon passing the last sensor, the cavity number is fed to the read-out and/or further processed.