Make reach to all components comfortable for any seated or standing user. Accommodate variations in hand and grip size. Provide adequate space for the use of assistive devices or personal assistance. Although direct accessibility to products, services and systems is by far the best solution, the type or severity of some persons' impairments preclude their ability to use a product even if it has been designed to include as many access features as practically possible. In these cases, special assistive devices, consisting of hardware, software or both, are required in order to make it possible for the user to access and use the product.
Examples are speech synthesizers, enlarged keyboards and software for screen magnification.
In many cases, these devices replace standard input and output devices. The standard hardware and software should therefore be designed to facilitate the connection of, interaction with and use of assistive devices. Nordic Guidelines for Computer Accessibility.