A method for evaluating calculator interfaces

Calculators have traditional user interfaces that no longer fit with acceptable practice in user interface design. This paper proposes a method for evaluating calculator user interfaces and demonstrates its value on a radically different style of calculator. The method produces a strong correlation between prior competence of the user and the time taken to achieve tasks with a given calculator despite differences in interfaces. Using this method, new calculator designs could be effectively evaluated and hence lead to long term improvements in their design. 1 The problem with calculators In this paper, we consider basic four function calculators, that is, ones with the four arithmetic functions together with one or two extra facilities such as a memory, percent and square root. The user interfaces for such calculators has remained reasonably static for the last thirty years. This is exemplified by the two Casio calculators 101-F and HS-8V showing in Figure 1. The former was released in July 1975 [3] and the latter is still on sale at the time of writing (late 2002). Both have the four arithmetic functions, square root, memory facility working with the MC , MR , M+ and Mkeys and a % key. With such a long history and the huge advances in both technology and in understanding usability, it would be hoped and expected that the calculator interface was well matched to usability requirements. This is not the case and we consider some examples from the HS-8V. A simple usability criterion [5] is that the user receives feedback on the state of the system. On picking up the HS-8V calculator when it shows Figure 1: The Casio 101F (left) and the Casio HS-8V.