The following three considerations are general techniques that should be followed:
1. Usually only two FAST diagrams are of interest: the diagram that represents an existing plan, program, or design, and the diagram that represents the proposed concept. When diagramming something that exists, be sure not to slip off on a tangent and include alternatives and choices that are not present in the existing system.
2. When using a FAST diagram to design or propose a new concept, restrict it to a specific concept; otherwise, the answers created in diagramming become meaningless. The “method selected” to perform a function brings many other functions into existence. Therefore, creation of several FAST diagrams during system design is a possibility.
3. The choice of the level of detail of functions to be used in the FAST diagram is entirely dependent on the point of view of the diagrammer, the purpose for which it is to be used, and to whom it will be presented. For presentation of VE study results to management, a very detailed FAST diagram should be simplified.
10.5.2 Summary of FAST Diagramming
1. FAST is a structured method of function analysis that results in analyzing the basic function, establishing critical path functions and supporting functions, and identifying unnecessary functions.
2. FAST diagrams should be constructed at a level low enough to be useful, but high enough to be advantageous to the purpose of creatively seeking alternative methods.
3. FAST diagrams are used to communicate with subject matter experts; to understand the problems of specialists in their own profession; to define, simplify, and clarify problems; to bound the scope of a problem; and to show the interrelated string of functions needed to provide a product or service.
4. The FAST procedure will be useful only if thinking outlined in the steps to prepare a diagram is performed. The value of this technique is found not in recording the obvious, but in the extension of thinking beyond usual habits as the study proceeds.
5. A FAST diagram, as first constructed, may not completely comply with “how” and “why” logic. This is because it takes additional thinking to get everything to agree. However, when you are persistent and insist that the logic be adhered to, you will discover that your understanding has expanded and your creativity has led you into avenues that would not otherwise have been pursued. When the “how” and “why” logic is not satisfied, it suggests that either a function is missing or the function under investigation is a supporting function and not on the critical path.
6. A main benefit from using FAST diagramming and performing an extensive function analysis is to correct our ignorance factor, so that we can see the study in its true light. Once this function analysis is performed on a given topic, we can quickly see that the only reason a lower-level function has to be performed is because a higher-level function caused it to come into being. Essentially, whenever we establish one of these functional relationships that is visually presented by a FAST diagram, we correct our ignorance factor and open the door to greater creativity.
