Descriptions - Mechanism and Process

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Adapted from Pocket Book of Technical Writing for Engineers and Scientists
by Leo Finkelstein, Jr.1

Being able to describe something accurately, in a way that your reader can understand, is an essential skill for a technical writer. Sometimes you will have to describe a thing — this is called a mechanism description. At other times you will have to explain the steps in a process — this is called a process description. Often you will have to do both. Let's review some of the strategies technical writers employ when they write descriptions.

A mechanism is a device with at least two parts that work together to do something. Some things are quite simple, while others are enormously complex. To describe a mechanism, first provide a technical definition and state the mechanism's purpose:

A cooling fan is an electromechanical device that uses an

electrically-driven propeller to move air. Today, many devices, including personal computers, generate substantial amounts of heat during operation. The heat must be dissipated in some way, and the most common way to move heat out of a computer

system is active air cooling using a fan.

Then focus on its physical attributes: size, shape, color, and material. You may use visuals to help you. For example:

A typical cooling fan is square in shape and measures 92mm diagonally.

The housing is made of black injection-molded ABS plastic. Each corner has a mounting hole, allowing the fan to be installed into a chassis with the help of screws

or rubber stems.

Next, list its parts in the order you wish to describe them. Then, describe the first part, and follow the pattern you have established with all the remaining parts. Summarize the mechanism's function in a conclusion. Most descriptions of mechanisms contain many labeled visuals to help the reader follow the text.

Processes are events that occur over time and have an outcome. Technical writers often have to describe a process. Doing this differs from the preparation of a mechanism description. In a process description, we focus on what a mechanism does. Again, we begin with a technical definition of the process:

Active cooling is based on forced heat transfer, i.e. passing cool air

over a heat-generating component(s), as opposed to passive cooling, where the heat is dissipated by pure convection only. Air is moved through the system by a cooling


Then, describe the function of the process. List the steps on the process. Then, beginning with step one, describe each of the steps in the process in chronological order. You will use descriptions throughout your writing in EG. Practicing effective techniques for describing mechanisms and processes will help you throughout your career.


1 Finkelstein, Leo, Jr., Pocket Book of Technical Writing for Engineers and Scientists. Boston: McGraw-Hill, 2000

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