" ... we can think of the machine as having two connections with the operator. Firstly there are the controls which can be acted on; and secondly, the displays which the operator can read, look at, or even feel. Feel is part of the display, and that's the word that psychologists use. The display from the machine will include the dials, the meters - anything from which the operator can collect information. And that includes hearing, listening to it, or vibration. Feel and vibration from your motor car is similarly a display back to you as the driver or controller of the machine.

So, today we are going to look more closely at displays and controls - and both these technical terms are the ones which psychologists have used as chapter headings in books on human factors or defining ways in which you communicate information to the person or from a person. Let's look at a telephone. What category does that fit into? Is a telephone a display or a control? Well, the ear piece is a display and the mouth piece into which you speak becomes part of the control. The two pieces are a display and a control because your voice command may be used to control the machine or the system. In a military environment it's not uncommon to have a very complex system at a space launch, then voice communication is an important part of the system. If someone mishears what you say, then of course they may do something wrong. I could tell you some stories about that, but we'd better keep moving ..."