Every time we enter a room, we are met with at least one physical affordance. When you enter a room and find it without light, the first thing you reach for is the light switch. Because lights in are usually operated by switches, you know there are usually two options: on and off. The physical design of the switch doesn’t give you any other choices. Buttons work in the same manner and in several European countries you will find that instead of switches, they have buttons.
Dials, on the other hand, let you know that they is more than just two options. They usually come in a circular shape that lets you know that you have to turn it to make a choice. Because dials give you more options that buttons and switches, they are often used for things like thermostats, air conditioners, and stoves. In both cases, the physical shape of the object we interact with gives us an idea of what it does.
Romantek 