I want to begin a discussion of minimum functionality for maximum usability, or mf = mu. It is obvious that the simpler an item, the more usable it should be. For example, think of the simplist writing instrument you can. For my part, a crayon or piece of chalk comes to mind. Each is as simple as it can possibly get. Especially when compared to other writing instruments.

The pencil for example has the drawback that the lead is buried in its body. Thus another instrument—a sharpner—is needed if the marking mechanism breaks or wears down. On the other hand, the marking mechanim of both crayon and chalk actually exists as the body of each item. Thus, as the point wears down, the marking ability continues.

Both crayons and chalk also excel past other types In terms of how easy it is to make marks. Some writing instruments, such as the fountain pen, rely on specific directional movements in order to work. You cannot make intentional marks with a fountain pen by putting the point against a surface and moving it in a upward, vertical stroke because it is only designed to release ink with downward strokes.

Chalk and crayon, on the other hand, can produce marks multidirectionally, and at any given angle (unlike a ball point or felt tipped pen).

These writing instruments are so simple, in fact, that they are typically the first writing instruments used by children, because they do not depend on a firm and complex grip or stroke to be used. Thus, they are perhaps the most usable of writing instruments.

However, crayons and chalk are light on functionality. Neither is permanent, neither is considered a “proper” writing instrument for professional contexts, neither is durable, neither can easily produce the clean look that a “fine” point is able to, neither possesses the aesthetic qualities of more expensive writing instruments. Thus, as functionality decreases, the usability of the product increases, and vice-versa.

This concept is not new, and most will think it pretty intuitive. And it is, as it derives directly from two concepts common to engineering design standards. These two guidelines are:

• Simplicity: the fewer the number of parts/complexity of parts, the better.
• Manufacturability: how easy is it to recreate/mass produce the design.

Now it's all well and good to talk in terms of pencils, pens and crayons, but what about more high-tech products? How may modern technology demonstrate this principle? Next we'll discuss two specific products that make use of the principle of minimum functionality for maximum usability. These two items are the iPod and Linux.