Labels and instructions
Labels on or around the terminal need to be positioned so that they can be comfortably read. This requires adequate illumination without unnecessary reflections.
Users need to be able to position themselves so that the text is in focus at the distance they are reading; bifocal spectacles are usually prescribed for reading at about 30cm and for distance viewing at over 1 metre. Therefore, the user may need to get their eyes to within 30cm of the text; this can give particular problems for tall users or those in wheelchairs.
Directions and Techniques
The instructions may need to be provided at more than one height to allow for tall people as well as people in wheelchairs.
Labels need to be positioned so that they are not obscured during use; it is necessary to allow for people who are left-handed.
Labels need to be designed so that the visual contrast does not deteriorate over time despite possible vandalism.
Numbering instructions in the order in which they need to be done can be beneficial for many users. This is particularly important if the sequence is not left to right or top to bottom.
- Make icons highly discriminable.
- Do not overlap icons.
- Do not differentiate by colour alone.
- Be consistent in the design of icons.
- Icons should be easily comprehensible.
- Label icons consistently.
- Animation should not reduce visual discrimination.
- Animate within icon boundaries.
- Keep animations simple.
- Do not animate automatically.
- Offer a summary or outline of a page.
- Present information in a logical order.
- Use different voices for different interface elements.
- Do not exceed 160 words per minute.
- Present messages serially.
- Experienced users should be able to reduce the number of prompts.
- Eliminate non-relevant speech.
Non-speech audio output:
- Use real world sounds whenever possible.
- Use a clear and easily understood metaphor.
- Keep auditory icons (often referred to as earcons) as short as possible, such as a sound for incorrect data entry.
- Put a gap between consecutive auditory icons.
- Provide active training or an intelligent help facility.
Vibro-tactile icons communicating sound through physical contact with the skin:
- The human skin is most sensitive around 250Hz, and stimuli should be between 50 and 400Hz.
- Do not use more than 4 intensity levels.
- Do not use more than 9 frequency levels.
- Ensure that the stimuli are not painful after prolonged use.
- The user should be able to adjust the stimulus intensity.
- Provide a facility for turning off tactual output for users who find it annoying.
- Minimise audio noise from the tactual display.
Kinaesthetic output providing a physical system response:
- Ensure that the output is easily discriminated by the potential users.
- Provide exploration strategies.
- Provide navigation information.
- Users often concentrate on a single modality and ignore the other modalities.
- Older users can find multimodal presentations confusing.
How you could check for this
Test terminals in a variety of environments taking into account changes in environmental conditions (e.g. Bright sunlight making labels and screens difficult to read). This may be particularly useful for terminals located outdoors.
During development, test with representatives of user groups in realistic situations.
During testing. The following key checks should be made:
- Labels are positioned for easy reading;
- Labels are legible for users with low vision;
- Numbered instructions are available;
- Icons are simple and meaningful.