The Buffer Trend report is the primary vehicle for assessing whether inventory is being managed in an optimal way. This report displays Date along the horizontal axis. The left hand vertical axis is the % of parts in each buffer zone while the right hand vertical axis is inventory value (from the raw materials cost). The number of parts in red, yellow, green and blue zones are calculated and displayed in the stacked column for each day.
While the goal of DDMRP is to achieve a high % in the green zone, followed by the yellow zone, with traces of red and blue, most implementations start with too much red and blue. The number of parts in the red zone can be reduced by placing supply orders as recommended by R+, while the blue zone can be reduced by canceling supply orders, and/or depleting quantities on hand.