The potential users:
Include people over 40 years old?
Include people with low vision?
Include people who are blind?
Include people with impaired colour vision?
Include people with a poor sense of touch (e.g. diabetics)?
Include people with poor manual dexterity?

Learning to use the system:
Instruction book in large print and on audio tape?
Learning mode for system?
telephone service to help confused customers?

Does the control system require:
Operation in low ambient illumination?
The user to see objects both at a distance and close to?
Multi-tasking by the user?
Users to respond within a preset time?

Have you incorporated:
Labels on controls which are of sufficient size in an appropriate typeface?
Labels perpendicular to user's line of vision?
Labels which can be read by a left-handed person using the controls?
Icons which are meaningful to a naïve user?
Indication for which input keys are currently active (eg by internal illumination)?
Colour coding which is differentiable by people who are red/green or blue/yellow colour blind?
Knobs or levers which can be controlled easily by all the potential users?
The ability for operation using only one hand?

Does the system have:
Logical layout of controls?
Consistent user interface?
User configurable interface?
Minimal time delay between control operation and feedback?
Auditory signals for priority inputs?
System reset to default settings?

Does the input include:
Tactual coding of keys?
Raised dot on 5 on numeric keypad?
Keypad conforming to EN 1332-3?
Visual indication of position of control?
Tactual and auditory feedback of key press?
Speech output of key press?
Speech recognition for commands?
Infrequently used keys positioned to minimise confusion?

Does the output have:
High contrast display?
Text on plain background?
No scrolling or moving text on the display?
Option of speech output of text on screen?
Volume control for speech output?
Headphone socket for speech output?
Audible output < 3 kHz?
Standard interface (possibly infra-red or radio) to alternative controls or displays?