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In all the ineventory control policies introduced so far, the review periods are taken to be constant and independent from the inventory level. In the classical (s,S,T) policy the length of all periods is constant and equal to T time units. Recent methods takes the duration of the first period different from the others, but steel a constant.
Obviously, the inventory level has a direct economical effect on the periods length. This paper describes a new control method of inventory systems in which the length of the review periods are calculated as a function of the inventory level. If the level at the beginning of a period is i, the period’s length is taken to be ?(i). Then by this method, the annual cost for given s and S becomes a function of ?(i), which is minimized with respect to ? . The result is the optimal valure of ?(i), namely ?(i), for any .