Mean Ceramic Date (MCD) An estimate of the center of gravity of the period over which an assemblage accumulated. Computed as the weighted average of the manufacturing span midpoints for a suite of ceramic types present in an assemblage. The weights are the frequencies of the respective types. This gives greater weight to the manufacturing midpoints of the more frequent types. The formula is: where xi is the manufacturing span midpoint for the i'th type and fi is its frequency. In DAACS, MCDs are computed using mean-ceramic-date types.