Short-term MRP is typically based on the sequence of customer orders. Most auto makers use some sort of frozen zone (ranging between 3 and 12 days), in which only minor order amendment is possible. The short-term horizon is supported by a scheduling of call-off signals for suppliers based on weekly and daily production sequences. Several reasons for changes in order sequence and the resulting volatility have been studied by Childerhouse et al. (2008). The short-term MRP function has no real scheduling task because there is nothing to decide and it serves only as a “translator” between dependent and independent demand (Meyer,2004).