Analytical designers must examine each component within a system to ensure that it is optimized for the duty it must perform. Failure or weakness in any part of the design can jeopardize the success of the product in the marketplace, since design modifications during the later stages of the design process are extremely expensive.

In reviewing the design of a component, some general questions to ask are:

	Will the material specified be the most economical for the part?
	Can the part be fabricated at an adequate production rate?
	Will the physical shape lend itself to processing at the minimum cost and an adequate rate or volume of production?
	Do dimensional tolerances permit selection of the most economical production methods?
	Is the part design based on consideration of scheduled production volume?

Analytical designers incorporate into their systems those components that maximize the ratio of effectiveness to cost, where effectiveness is the ability of a component or system to perform its intended function when it is operating in accordance with the original design concept. For example, assume that a device is required to convert rotary motion to rectilinear motion. The "black box" for the component is represented in the figure, and the following devices are being considered to perform this function:

	Cam-and-follower
	Rack-and-pinion
	Power screw (or ballscrew)
	Slider-crank

The analytical designer must first determine how well each mechanism fulfills the technical design requirements. Such an analysis might eliminate some of the alternates from the list. The final choice, though, would be made by comparing effectiveness-to-cost ratios such as mechanical efficiency to cost, life to cost, or power per pound per dollar.

To evaluate a complete system, consider areas such as these listed below for possible cost savings (these are examples appropriate to a manufacturing environment):

1. Selection of materials.

2. Choice of fits, limits, and tolerances between parts - generally, costs increase rapidly as the degree of precision is increased.

3. Selection of plain bearings versus anti-friction bearings - anti-friction bearings are often used for low-volume productions while inexpensive plain bearings are used in high-volume production.

4. The quality of insulation used to reduce noise.

5. The type and amount of thermal insulation, and the associated size of pipe or duct employed.

6. The degree of precision or quality of purchased parts - a common example is the replacement of a low-class (low precision) ball-bearing with an equivalent high-class ball bearing. Here a significant increase in life (effectiveness) can be realized but only with a significant initial cost penalty. We trade off initial cost for performance, and the effectiveness-to-cost ratio may increase or decrease depending on whether the cost factor reflects the total cost.

7. The quality of surface finish employed - this can have a significant effect on cost. If hand finishing is required the added cost is notoriously large, but a high-grade finish can have a significant effect on the fatigue life of a critically-loaded part. 8. the type and amount of plating and/or painting which is used to protect a component in an adverse environment. In general, this leads to large, but necessary, additional costs.

Economy is also closely associated with production volume and with the manufacturing process. The best choice of manufacturing processes depends on the projected production volume and the desired market life. Production volume is usually divided into three categories:

	One-of-a-kind
	Low-volume manufacturing (less than 250,000 units per year)
	High-volume manufacturing (more than 250,000 units per year)

When a one-of-a-kind machine is produced, as little as possible should be spent on tooling, since hand made parts are very expensive. Standard or purchased parts usually represent at least 60 percent of the total costs under these circumstances. In fact, even low-volume products parts should be designed so that they can be manufactured on standard tools.

If high-volume production is indicated, only then can expensive tooling be amortized effectively. The effectiveness of forging parts, for example, can be realized because the volume of production can easily produce the necessary money to amortize the high initial cost of the forging dies and forging machine tools.