the inventory level and the instantaneous flow rate is the material requisition rate.
Inventory is measured in units. Material requisition rate is measured in units per unit
time (e.g. units/day). The required inventory is a constant. The difference between
the required inventory and the actual (existing) inventory is the inventory discrepancy (or deficit).
Inventory discrepancy is an auxiliary variable. Information on desired inventory
and on actual inventory is necessary to define this variable. Thus, it obtains
Desired
inventory
Inventory
Inventory
discrepancy
Material
requisition
rate
Time to meet
inventory
discrepancy
Fig. 6.4 Information flow connecting a level to a rate
Men in
training
Training
completion
rate
Training
manpower
Men
leaving
rate
Average length
of service
Average training
time
Hiring
rate
Production
rate
Inventory
Shipment
rate
Labor
productivity
Fig. 6.5 Information flow joining two dissimilar physical flows
178
6 Infrastructure as a System