Usability Principles

1. Make systems easy to use, Keep the interface simple
Keep the interface simple because simplicity reduces the demand on users’ brain power and focuses users’ attention on the task

- Present information in meaningful groups according to how or when they will be used.
- Organize and present information or processes in a straightforward, simple manner. Group related information or processes together.

2. Provide proper search and navigation
- Make the interface consistent: When a User interface is consistent, it is easy to learn and users become familiar and comfortable with the program more quickly.

Maintain consistency in all aspects of the program, including:
• screen layout,
• navigational elements,
• use of language, graphics, and sounds,
• metaphors
• feedback mechanisms.

- Provide feedback
Provide informative and timely feedback for every action. If the users move the mouse, the cursor moves. If they type on the keyboard, the typed letters appear on the screen. Communication should be brief, direct, and expressed from the user’s perspective.

- Let Software be forgiving for user’s mistakes
By building in forgiveness, you will encourage users to explore the territory without fear of breaking or ruining anything. Users are more productive and confident with a program that they feel they can safely explore. Forgiveness encourages users to independently learn and explore.

- Offer multiple search strategies in on-line environments
You should provide flexible interfaces to accommodate the various factors involved with users searching for information.

- Let users search by browsing in hypertext documents
You should build support for browsing into an on-line hypertext system, since most users, especially novice or infrequent users, prefer to browse for information rather than use analytical search strategies, which are generally planned and goal driven.

- Give users menus and maps that outline their choices
Users of hypertext report that a major problem is that they tend to feel “lost” or “disoriented”. This condition occurs when users do not know:
· where they are in the hypertext system;
· where they have already been (nodes visited); and
· where they can explore (options for movement).

Provide a proper outline for visited links with different color, breadcrumbs to show where they are. Provide visual clue to help users navigate. Also provide back track option.

- Use headers, footers to tell users where they are

3. Readability:Improve readability by designing effective page and screen layouts

- Don’t overload users’ working memory

- Give your layout an obvious structure
Here are some tips for using format design variables to create
screen layouts:
· Use headings systematically to assist the customer in searching for, retrieving, and comprehending the information.
· Use vertical spacing systematically to help the customer understand the structure of the text.
· Use typographic cueing to direct the customer’s attention and to express the structure of the material.

- Divide text into logical ‘chunks’
Organize textual material into logical and conceptual “screenfuls” that take into account the size of the screen and the limitations of the user’s working memory.

- Use color to enhance cognitive processing
Use color to help structure the content and guide a customer through these displays. Researchers suggest using color to:
· enhance the “personality” of the different functional areas,
· distinguish between different types of information,
· establish a link between related pieces of information,
· highlight important or critical messages, and
· help customers understand complex displays.

- Provide quotes, questions, or photos to support the text
Provide accompanying material, such as quotes, questions, or photos, to increase the reader’s understanding of and interest in the text.

4. Use words readers can easily understand

- Use common vocabulary
Use familiar vocabulary that occurs frequently in everyday text. Readers will find it easier to read, process, and recall a passage if the words are familiar.

- Avoid abbreviations, acronyms, and initialisms
Although abbreviations, acronyms, and initialisms may save space, you should avoid them unless you are certain that readers will know the terms for which they stand. Consider the level of knowledge and background of the readers.

- Use headings to present key ideas and provide structure
Headings can help readers recall, search, and retrieve information from the text. Headings also act as signaling devices, directing the readers’ attention to important or key ideas. Headings also help readers understand the text structure, which stimulates learning and lets them search for information
in a passage. Headings help readers avoid information overload.

Benefits and drawbacks of using pixel, point, percent, em units

As a web developer, we may have came across, questions like
- Which unit to use for measurement?
- What is the relevance of each unit?
- Pros anc Cons of using them

Lets talk about each units in detail.

Most commonly used units for measurement are as follows :-

- Points (Absolute measurement unit)
- Pixel (Relative measurement unit)
- em (Relative measurement unit)
- percent (Relative measurement unit)

Points:
This is absolute unit of measurement, and takes the absolute size based on user’s screen. To be more specific, based on resolution of the screen the font may increase or decrease, so this is not good for using in normal web pages.

When to use?
Points are good choice when we want to go for printing. So if you are planning to make a printable version of your page, make use of point units.

Pixels:
Pixels are relative to the screen resolution.This is relative unit of measurement and is good if we want to have better control of the web pages.

When to use?
If control over the look of your Web page is your biggest concern, then you should use pixels. Pixels are the standard unit of measure for screens and monitors, and fonts will be more precisely the size you want on the screen.

em:
This is relative unit of measurement. em is good for accessibility. We should use em when we want to make our application accessible. Drawback of em units is that font size is relative to standard size of browser, so we lose control over the exact look of the web page.

When to use?
If accessibility is your biggest concern, then you should use ems. Ems are sized so that the font size is relative to the parent element. Using ems ensures that your pages will be accessible to most browsers and platforms. Also if your readers choose to change the default font size of the page, your page will scale to that new size.

The problem with ems is that you lose control over the exact look of your page.

Percent:
The percentage value is relative to the surrounding text or the user’s default font, so when you define a font size with the value 50 percent, and the default font size was 16px, you get an 8px font size.