Given that in any particular analysis the flow unit could be a loaf of bread, a pound of flour, a revenue dollar etc. etc. there are also many reasonable choices for the entry and exit of the flow unit into the process analysis. The authors state that it is important to note the process is defined by choosing an entry and exit point and a flow unit, which means that:

all answers are likely to be correct in their own way

each process definition leads to different values for throughput

each process definition leads to a unique value for flow time

each process definition leads to a different value for inventory

each process definition leads to unique values of throughput, flow time and invetnory