The [average period of production] is crucially dependent on being able to identify the stages of production. It is assumed that the process begins at stage 1 and ends at stage
n. In this way any kind of “looping” (coal is used in the production of iron and vice versa), where the output of one stage becomes available as an input of an earlier stage, is ruled out. Second, if the output is a flow (as it usually is), then we must also have some way to connect inputs that occur at time periods
n—t with precisely that output that arrives at time period
n and separate them from those that need to be connected to outputs occurring at time periods
n+j where
j is an index of time periods occurring after n. In other words, if the production process is a
flow input—flow output process, a set of inputs are used to produce jointly a set of outputs occurring over time and the measuring of
T becomes more problematic. Similarly, we must be able to identify the amount of labor time
l that is used. This obviously presumes that it is possible to reduce any labor heterogeneity to comparable terms, like efficiency units, and then to measure the number of such units supplied per period of time.
#