1.3. The use of MRP
Fifteen of the companies using MRP were making use
of recognized software packages supplied bya vendor;
eight had developed an in-house system designed by a
consultant. Nineteen used the same inventoryrecords
(e.g., gross requirements, scheduled receipts, projected
on-hand inventory, net requirements, planned order
receipts and planned order release). Four had introduced
additional inventoryrecord s.1 Eight of the
companies accepted a computer statement, and 15
accepted a computer statement onlyafter reviewing it.
None used manual calculations alone.
Global competition means deliverybeco mes increasinglyimpor
tant. Lead-times for purchased items are
determined following negotiation between the purchasers,
within the companyan d with its suppliers. Thirteen
of the companies using MRP companies arrived at their
lead-time byagreem ent and five used past data, based
on their knowledge of the market and up-dated it if
change occurred. The others used both methods.
Anderson et al. (1982) suggest that most (70.4%)
MRP users work in time buckets2 of one week. But here
onlyfiv e companies used the MRP monthlytime bucket.
Six applied weeklytim e buckets because of the volume
of items involved, or theyused weeklytim e buckets
for ‘short jobs’ and monthlyfor ‘longer jobs.’ Twelve
companies worked in days because of the batch quantity
of their workload demand. The most popular planning
horizon was a year or less; only five used a three-year
horizon, and another five used a 1–6 month period. Two
companies used a two-year horizon.3
To enable MRP to carryout its explosion, the
formulas for lot sizing must be part of its computer