Please note: This section of the guidelines focuses mainly on mechanical keys. We also have a section specifically referring to membrane keys.
Consistency in the layout of keypads is essential for blind users and highly desirable for other users. It is also important to set out the keys in a way that makes it easy to distinguish between the main numerical keys and other function keys. Variation in the size, shape and position of function keys will help differentiation.
A standard layout for keypads is essential for blind people. There are currently two common layouts for numeric keys; the telephone layout and the calculator layout. It is recommended that the telephone layout be used exclusively on public access terminals.
Enlarged raised keys enable persons with poor dexterity to press the correct key; a concave shape to the keys will also help fingers to stay in place. However some disabled people prefer convex keys since they can be activated by the hand for those unable to use their fingers. The spacing between the keys is as important as the size of the keys. When a person has difficulty making precise finger movements, large keys that are recessed or guarded can help ensure that the wrong key is not pressed. For many disabled people it is important to be able to connect an external keyboard to suit their specific needs.
On a telephone, speech-input keying is a useful means of providing a hands-free call set-up for users with reliable voice, and may be valuable even where full hands-free operation is not necessary (eg when hand tremor interferes with manual keying). Useful for dyslexic users who can read aloud and simultaneously dial a number thus avoiding short-term memory problems. Such systems could be limited to just the numerals or a few words such as 'doctor' or 'Jane'.
Large clear typefaces should be used to improve legibility for persons with low vision. When choosing typefaces it is important to use characters that have clear 'open' shapes. Many people with low vision can easily misread such characters as 3, 5, 6, 8 and 9 if the tails curl over; this tends to blur or merge the shapes. There is a typeface specifically developed for labelling keys.
Visual markings on the keys should be characters at least 4 mm high and should have good contrast with the colour of the key (eg. white characters on matt black keys). However, on numeric keypads which also include up to 4 alphabetic characters, the size of the alphabetic characters should be as large as possible without affecting the legibility of the numerals (NB for most users, the legibility of the numerals is more important than the legibility of the alphabetic characters); the spacing between the alphabetic characters is as important as the size of the character.
- Colour coded keys should be:
Red: Cancel Yellow: Clear or Correct Green: Enter or Proceed Blue: Help or Information
The standards in various countries differ over the embossed symbols to be used on the function keys.
The most prevalent are:
Controls and keys should be tactually discernible without activating the control or keys. The status of all locking or toggle controls or keys should be visually discernible, and discernible either through touch or sound.
The arrangement of keys
Function keys should be clearly separated from the numeric keys. When command keys are vertically arranged, 'cancel' should be the uppermost key and 'enter' the lowest. When the command keys are horizontally arranged, 'cancel' should be located the furthest left, 'enter' the furthest right. It is better to position the command keys to the right of the numeric keys. They are then less likely to be inadvertently touched when entering numerals. Where command keys are positioned beneath the numerical keys they may pose a problem to visually impaired persons because they are likely to be pressed accidentally when entering numbers. Command keys should be as large as possible so that the words on them can be larger and thus easier to read.
Colour should not be the only distinguishing feature between keys, since red/green colour blindness is not uncommon; if possible, the keys should have different shapes and be marked with symbols.
Internal illumination: visual benefit
Results of a study into the benefit of internal illumination reveal that a benefit exists in lower ambient lighting conditions, such as a shaded cash machine, an indoor ticket machine, an underground car park, or a covered petrol station, where artificial lighting may be low or non-existent. In contrast, in bright ambient lighting, a slight disadvantage to having internal illumination was revealed (when compared to a non-illuminated keypad with white text on black keys). The darker the ambient lighting, the more beneficial internal illumination of keys will be.
Tactile indication can be provided by a gradual increase in the force, followed by a sharp decrease in the force required to actuate the key, and a subsequent increase in force beyond this point for cushioning.
Many elderly people and those with a cognitive impairment do not like to be rushed or to think that they are likely to be 'timed out' by the machine, so it is necessary to allow for such people to use the terminal at their own pace; this requirement could be stored on the user's card.
Keypads are often used in security context, therefore they often need to be hidden from the view of others. This can be achieved by the addition of a privacy shield. Since the principle purpose of a privacy shield is to block the keys from view, this can pose serious problems with respect to accessibility, both visually and physically. Our section on privacy shields provides further information on these accessibility issues.
- Designers should follow the ETSI standard ES 201 381 for tactile identifiers on keypads.
- The user should have the option of pressing keys sequentially instead of simultaneously (eg having to press a control key at the same time as a numeric key).
- Raised keytops should be concave.
- Legends should be high contrast to the colour of the keys.
- Provide feedback for each key's actuation.
The following are drawn from other guidelines but the scientific data on which they are based are not quoted:
- Keys should be at least 15mm wide by 15mm high.
- The spacing between the keys should be at least 50% of the width of the key.
- There should be at least 3.2mm spacing between keys.
- There should be at least 9.6mm between function keys and a numerical keypad.
- The force required to operate a key or slider control should not be greater than 22.2 Newtons (irrespective of the orientation of the control). However, other guidelines specify a pushing force of not more than 2 Newtons.
- EBS100 V3 (October 2004) Keyboard Layout for ATM and POS PIN Entry Devices
- DTR/HF 02009 (1996) Characteristics of telephone keypads.
- EN 1332 Machine readable cards, related device interfaces and operations.
- EN 29241 Ergonomic requirements for visual display terminals.
- ES 201 381 (December 1998) Telecommunication keypads and keyboards: Tactile identifiers.
- ETR 345 (Jan 1997) Characteristics of telephone keypads and keyboards; Requirements of elderly and disabled people.
- ETSI DTR/HF 02009 (1996) Characteristics of telephone keypads.
- ETSI TCR-TR 023 (1994) Assignment of alphabetic letters to digits on push button dialling keypads.
- ETSI ES 201 381 (December 1998) Telecommunication keypads and keyboards: Tactile identifiers.
- IEC 73 (1990) Colours of pushbuttons and their meanings.
- ISO 9564-1 (2002) Banking - Personal Identification Number (PIN)
management and security,
- Part 1: PIN protection principles and techniques for online PIN verification in ATM and POS systems, Informative Annex E Additional guidelines for the design of a PIN entry device.
- ISO DIS 9355-2 (1999) Ergonomic requirements for the design of displays
and control actuators.
- Part 1: Displays.
- ISO/CD 9355-1 (1999) Ergonomic requirements for the design of displays
and control actuators.
- Part 1: Human interaction with displays.
- ISO/IEC 9995 (1994) Information technology: Keyboard layouts for text and office systems.
- ITU E161 Arrangements of figures, letters and symbols on telephones.
- ITU-T E.902 (1995) Interactive services design guidelines.
- Part 3 Keypads.
- Part 4 Keyboard requirements.
- TCR-TR 023 (1994) Assignment of alphabetic letters to digits on
push button dialling keypads.
- Guidelines for Designers of Public Access Terminals
- Designing User Interfaces for People with Visual Impairments