Design of Tables

• Whether data should be presented in columns or rows depends on what is more natural for the task in question.

• Letters are better for identification than numbers.

• Numbers should be arranged in as few columns as possible.

The design of pictures and the positioning of text within each frame is usually a compromise between several different factors. It is usually very difficult to adhere strictly to the various criteria that are set in designing different frames.

The design of frames or pictures is also determined by the length of the text, as there is only a limited area available; if the text is very long, its length will determine its positioning. In such cases it may be necessary to abbreviate the text. When doing this, it is of the utmost importance to maintain as far as possible the comprehensibil­ity of a word even though it is abbreviated.

Through the placing of the same information in the same position in different frames, the possibility of errors by the operators is reduced, together with search time. This is particularly true for beginners and those who use the terminal infre­quently. Consistent positioning of error messages is also very important as they must always be immediately obvious to the operator. Messages may be overlooked if the operator has to search for them.

The most fundamental criteria by which information to be used in a frame should be analysed are:

1. The importance of the information.

2. Its frequency of use.

3. The sequence of use.

It is clear that even though these criteria have importance on their own, they are very closely connected. One example of this is the first information to come up on the screen, which is often both the most important and the most frequently used information.

When the principles for the design of the pictures and the text have been deter­mined, the information should be presented in such a way as to simplify the task of the operator as much as possible.

Formerly, the CRT type of display used to have poor picture sharpness (focus) at the perimeter caused by the curve on the screen edge, which reduced the visual clarity of the characters. On many screens, this may mean reducing the amount of information on both the left – and the right-hand sides of the screen by three, four, or even five columns in order to avoid this poor focus area. The effective area of the screen is thus reduced. Another aspect of the design is whether to use every line or every alternate line. No general answer can be given to this, as it depends partly on the design of the screen (that is, the distance between the lines) and partly on the amount of information on the screen. Apparently, the modern generation of CRT has solved most of these problems. However, the continued usage for 24 hours per day, 365 days per year, does create problems for all types of displays and the user.

After determining the above criteria comes the question of how tightly together the information should be positioned. The amount of information may be defined as the quantity of information within a defined area. If too much information is dis­played, operator performance is decreased (Stewart, 1976; Cakir, Hart, and Stewart, 1979). Stewart suggests that the search time in seconds is roughly one-fifth of the number of alternatives to be searched through. Even if a very experienced operator is able to be selective in searching for information, irrelevant information means that the search time and error frequency will increase, thus reducing the performance of the operator and the system.