The following pages give some examples of controls and their usability by someone with little or no vision. It is important that the user can reliably operate the control as well as determine the status with a minimum of errors. Auditory and tactual feedback can help users be confident that their command has been accepted.
Lever switch
A lever switch usually has two stable positions, but it can have more. If mounted vertically, then the UK convention is for 'down' to be 'on'. But if it has multi-positions, then 'down' is for minimum value and 'up' for maximum value. If a multi-position switch is mounted horizontally, it can be less easy to operate by someone with reduced strength in their hands. A long lever arm can be used by someone with poor manual dexterity or a hand tremor. With the bistable switch, its position can be easily determined non-visually.
Rocker switch
It can be difficult to visually determine the status of a multi-position rocker switch. A contrasting colour can make it easier to see the position of a bi-stable switch. For someone with poor manual dexterity, feedback that audibly or visually shows the status can help.
Press button
The control can be activated on either the push or the release action. Tactile indication can be provided by a gradual increase in the force, followed by a sharp decrease in the force required to activate the key, and a subsequent increase in force beyond this point for cushioning. If the top of the button is concave, then the finger is less likely to slip off the button. With numeric keypads, the convention is to have a raised dot on number 5; however this does not help differentiate between the telephone and calculator layouts.
Pull switch
The advantage is that it is less easy to accidentally activate than a push button switch. However it may require a strong grip if the switch is stiff. There may be no direct indication as to the status of the switch; for instance if the bulb has blown in a bathroom light, there may be no way of knowing whether the fitting is live.
Touch switch
This can be a proximity switch (as in some lifts) or a touch panel (e.g. on a microwave cooker), but it requires the user to position their finger accurately. There are major problems for blind users since it can be very difficult to locate the control and impossible to know whether the control has been activated, unless there is an auditory signal. For touch panels, but not proximity switches, embossed markings can help identify the active area.
Slide control
For a blind person, it can be difficult to estimate the initial position respective to the two ends of the scale. For those with reduced strength, it is often less easy to operate a control which has to be moved from side to side. Small joysticks can be very difficult for users with a hand tremor.
Rotary control
The shape of the knob can act as a tactile pointer to the setting. It is not always easy to determine the 'null' position when it is not at the end of the scale (eg stereophonic balance control). For someone with poor manual dexterity, there can be a significant difference whether the knob's rotation is in line with their arm or at right angles to it. Knobs which require both pushing and turning at the same time can be particularly difficult for many elderly people.