Overview

JAKOB NIELSEN

Technical University of Denmark

One of the most important aspects of usability is consistency in user interfaces. Consistency should apply both within the individual application and across complete computer systems and even across product families. As a simple example of consistency, consider the three numeric keypads shown in Figure 1. Obviously the calculator keypad and the Danish telephone keypad are consistent, while the US telephone keypad is inconsistent with the other two.

Figure 1: Three different designs of numeric keypads. The calculator keypad probably has the oldest design, and Danish telephones were designed to be consistent with it while US telephones use another design.

The US telephone keypad was actually a good design when it came out because most people would have agreed then that so few people used mechanical adding machines that there was no need to take them into account when designing a consumer product for. the mass market. Now, of course, almost everybody has a pocket calculator and many people also use computer keyboards with numeric keypads. The Danish telephone companies lagged somewhat behind in introducing pushbutton telephones and therefore had the opportunity to make their design consistent with calculators.

Consistency can also be a problem within an individual interface. For example, the Macintosh menu bar consists of a number of pull-down menus with names as well as a single menu to the far left marked by an Apple logo. In several studies of novice users we have found that people do not tend...