A consistent system allows users to build mental models that will aid in the interaction and in the operation of the application. If consistency is missing, users have to rely more heavily on memorization instead of building and relying on mental models. When a user has a mental model of how the application performs the task, it will be easier for the user to perform his or her task.
A consistent system is easier to learn and use. To achieve consistency it is important that the development team of the application specify a set of conventions to be used during the development of the product. In the analysis phase it is therefore important to keep your eyes open for conventions followed in the present environment that can be moved into the new environment.
Here are some things that can help keep the interface consistent:
Lists of alphabetic data should be left-justified and numeric data should use decimal alignment, so that data without decimals are right-justified.