A pattern of exchange practices where the recipient of a supply of goods keeps a proportion and passes the rest on (trades, sells, gives as gifts, etc.) to the next group who do the same. The pattern repeats but the volume of material gets less with every transfer. If the volume of material is plotted on a graph against distance from source, such a pattern of exchange will appear as an exponential decay curve; plotted on a logarithmic scale the fall‐off appears as a straight line. See also distance‐decay model.