126 Operational Thinking 6.3.1 Critical properties of the process The most important element in our throughput scheme is identification of critical properties of the process. Time, cost, flexibility, and quality are usu- ally among the major factors that determine the success of a throughput process. They form an interdependent set of variables so that each one can be improved at the expense of others. Treating them as independent vari- ables, as is normally done, is an unacceptable mistake. Unfortunately, expertise is in any one of the areas of time cycle reduction, cost control or waste reduction, and quality control. Each expert tries to suboptimize the single area of her/his concerns by manipulating the process. This might lead to incompatibility among the solutions. The challenge is to reduce cycle time, while eliminating the waste and ensuring availability of the out- put (in kind, volume, space, and time), in addition to managing the pro- cess in such a way that it is "competent and in control" all at the same time. This can only be done by simulating the throughput process by building a dynamic model. 6.3.2 model of the process The model of a throughput process in its simplest form is a set of interre- lated activities designed to produce an explicit output. Different ways and several levels of sophistication can be used to model a process. The most common is a simple flow chart. However, to get a handle on interdepen- dencies and the dynamics of the system, I like to use the iThink software to simulate throughput processes. In addition, I believe Eliyahu Goldratt's (1997) constraint theory or more specifically his book, Critical Chain, is a must read and a fitting complementary tool to our throughput modeling formulation. In Critical Chain, Goldratt, by recognizing principles of multidimen- sionality and emergent property, demonstrates beautifully why local opti- mization does not lead to global optimization. Using the chain as an analogy for a throughput he asserts that the strength of the chain repre- sents the throughput of a process, and the weight of the chain represents its cost. Then he goes on to argue why we have lost the luxury of choosing between increasing the throughput or reducing the cost, why the old dichotomy is not valid anymore, and that to survive we need to increase throughput and reduce cost at the same time. Since the strength of a chain is defined by its weakest element, he pro- poses an iterative process of strengthening the weak links in sequence of the weakest link first. Each iteration improves the throughput to the next limit defined by the next weakest element with a minimum cost, thus eliminating the cost of over-designs. Then using his ingenious observation that time estimated to finish a task with 80% of confidence is three times greater than the most probable time it takes to finish the task (see Figure 6.23) Goldratt develops an