| Constraints | Examples |
|---|---|
| Physical | USB-A vs USB-C (USB-A has constraints unlike USB-C) |
| Cultural | Chopsticks (In some culture, people have hard time using it) |
| Semantic | Phone dial (For us, it's a dial pad. For grandma, it's a dial) |
| Logical | Lego (Only one piece left, only one place to go) |
Doors, switches
Physical mapping: Switches in the example are mapped along the layout of the floor
Activity centered controls: Video, computer, full lights... categorised depending on the activity. It is great in theory, but actually difficult to get it right. Cannot adjust for unexpected activities.
Forcing functions
- Interlocks : Oven's door does not open unless it's turned off. (dead man's switch) You have to keep pressing the button
- Lock-ins : The dialog asking if you want to save when you try to exist the app. Adobe products... Once they become standard, nobody leaves
- Lockouts : The gate at the ground floor to prevent people going down when they are panicked
Consistency is to be followed. If a new way of doing thing is only slightly better than the old, it is better to be consistent.
examples: Destination-Control Elevators, the metric scale of measurement
The elevator is faster, but cannot change the destination once you get in.
The measurement is commonly used, but a few countries still resist its use.
The change is too upsetting for the people who have to learn the new system
Sound is tricky. It can annoy and distract.
In web design, sound as signifiers is a bad idea because you don't know how users are setting their speakers
Sound when the car is backing up
Electric cars play sound as it's too quiet