Human–Computer Interaction — INTERACT’99 Angela Sasse and Chris Johnson (Editors) Published by IOS Press, c IFIP TC.13, 1999 1 Evaluating Gedrics: Usability of a Pen-centric Interface J¨ org Geißler 1 , Michele Gauler 2 & Norbert A Streitz 3 1 Plenum Systeme GmbH, Hagenauer Straße 53, 65203 Wiesbaden, Germany. 2 Johannes Gutenberg University, Institute of Psychology, Staudingerweg 9, 55099 Mainz, Germany. 3 GMD-IPSI, Dolivostraße 15, 64293 Darmstadt, Germany. Joerg.Geissler@plenum.de, gaulm000@mail.uni-mainz.de, Norbert.Streitz@gmd.de Abstract: Many users of today’s pen computers have an ambiguous attitude towards these devices. On the one hand, they like the ease of use, especially in the beginning. On the other hand, after some time, they often feel hampered by the systems since the user interfaces do not reflect the users’ individual skills, experiences, and preferences. Pen interfaces treat all users in the same way — like novices. Becoming an expert or ‘power’ user is quite difficult. In this paper, we report on the gedric approach (Geißler, 1995) to this problem and evaluate an application with a so-called pen-centric user interface(Geißler, to appear). We will show that such an interface efficiently supports experienced as well as novice users. By having the freedom to choose from two popular interaction styles — menus and gestures — and to mix them arbitrarily, gedrics support a wide range of user preferences and skills. This results not only in efficient individual working styles but also in a high user satisfaction. Keywords: pen computing, gestures, menu interaction, gedrics, usability, study evaluation. 1 Introduction A widely used statement in the research field of pen computing (Meyer, 1995) says that the pen is mightier than the mouse. In addition to pointing, people are able to sketch, annotate, gesture, and even write with an electronic stylus as they can do with pen and paper (Wolf et al., 1989). Unfortunately, today’s user interfaces for pen computers — so-called pen-based interfaces — only use a fraction of the capability of the pen. A small number of gestures is used for simple editing tasks but most of the interface is still based on traditional concepts like push buttons, pull- down menus or other point-and-click components. Strictly speaking, in these interfaces, the pen primarily simulates the mouse and just offers some neat add-ons in terms of gestures. Pen interfaces seem to ignore that pen interaction primarily is stroke-based, and not tap- based (Geißler, 1995). In the long term, those ‘gesture-enhanced point-and-click interfaces’ obstruct users who have become experienced or even experts because there are no short cuts for all the functions that are available. Users are forced to continue working with inappropriate interface components — see also (Grudin, 1989). Current pen interfaces may be attractive for inexperienced users, but they do not support their learning process and finally they still treat skilled users like novices. Extending the influence of gestures on the overall interface design is not that easy. Most of the time, studies about the usability of pen gestures restricted the number of gestures deliberately to ten or even less (Geißler, to appear). Gestures are only useful if they are easy to remember and this depends on their ‘naturalness’ or familiarity to users. For this reason, only very specific tasks have been observed. Evaluators admitted that the usability of gestures in other, more complex tasks or even in applications that are completely based on gestures, is not yet clear and require further observations (Wolf, 1992). An attempt to overcome these shortcomings is a user interface component that combines traditional interface concepts with pen gestures. Therefore, we developed the gedric (Geißler, 1995). It is part of a so-called pen-centric interface (Geißler, to appear) that also covers aspects like ubiquitous