According to the Center for Universal Design, headquartered in North Carolina State University, UD has seven basic principles.
Perceptible Information
The design should be able to show potential users the most important information that will lead to the effective use of the product, device or environment. Information should be made accessible regardless of the sensory capabilities of the user.
In the picture above a blind individual can use the cellphone's keypad because of the bump on the pad that will enable the user without looking at the keypad.
See 5. Tolerance for Errors
In the picture above a blind individual can use the cellphone's keypad because of the bump on the pad that will enable the user without looking at the keypad.
See 5. Tolerance for Errors