early work provided the foundation to the inventory
management literature frequently referred to as
independent demand management. It led to the
development of numerous reorder order point (ROP)
systems like base stock, continuous review, periodic
review, etc. Much of this work was done manually, using
pencil and paper, a slide rule or a simple tabulating
machine available during the 1930s and 1940s. The
approaches normally focused upon single level stocking
decisions, even though many companies were dealing
with multi-echelon material flow on the factory floor.